After a track fails, and I try to ctrl+c out of bst:
```
[00:00:21][????????][   track:pkgs/apps/nautilus.bst        ] BUG     Track

    An unhandled exception occured:
    
    Traceback (most recent call last):
      File "/usr/local/lib64/python3.11/site-packages/psutil/_pslinux.py", line 1653, in wrapper
        return fun(self, *args, **kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_common.py", line 480, in wrapper
        raise raise_from(err, None)
              ^^^^^^^^^^^^^^^^^^^^^
      File "<string>", line 3, in raise_from
      File "/usr/local/lib64/python3.11/site-packages/psutil/_common.py", line 478, in wrapper
        return fun(self)
               ^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_pslinux.py", line 1695, in _parse_stat_file
        data = bcat("%s/%s/stat" % (self._procfs_path, self.pid))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_common.py", line 813, in bcat
        return cat(fname, fallback=fallback, _open=open_binary)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_common.py", line 801, in cat
        with _open(fname) as f:
             ^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_common.py", line 765, in open_binary
        return open(fname, "rb", buffering=FILE_READ_BUFFER_SIZE)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    FileNotFoundError: [Errno 2] No such file or directory: '/proc/2463427/stat'
    
    During handling of the above exception, another exception occurred:
    
    Traceback (most recent call last):
      File "/usr/local/lib64/python3.11/site-packages/psutil/__init__.py", line 361, in _init
        self.create_time()
      File "/usr/local/lib64/python3.11/site-packages/psutil/__init__.py", line 719, in create_time
        self._create_time = self._proc.create_time()
                            ^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_pslinux.py", line 1653, in wrapper
        return fun(self, *args, **kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_pslinux.py", line 1863, in create_time
        ctime = float(self._parse_stat_file()['create_time'])
                      ^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/_pslinux.py", line 1660, in wrapper
        raise NoSuchProcess(self.pid, self._name)
    psutil.NoSuchProcess: process no longer exists (pid=2463427)
    
    During handling of the above exception, another exception occurred:
    
    Traceback (most recent call last):
      File "/usr/local/lib64/python3.11/site-packages/buildstream/_scheduler/jobs/job.py", line 438, in child_action
        result = self.child_process()  # pylint: disable=assignment-from-no-return
                 ^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/_scheduler/jobs/elementjob.py", line 91, in child_process
        return self._action_cb(self._element)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/_scheduler/queues/trackqueue.py", line 65, in _track_element
        return element._track()
               ^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/element.py", line 1390, in _track
        return self.__sources.track(self._get_workspace())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/_elementsources.py", line 97, in track
        new_ref = source._track()
                  ^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/source.py", line 1202, in _track
        new_ref = self.__do_track()
                  ^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/source.py", line 1430, in __do_track
        return self.track(**kwargs)
               ^^^^^^^^^^^^^^^^^^^^
      File "/var/home/adrian/Projects/build-meta/.bst/staged-junctions/junctions/bst-plugins-experimental.bst/7a4409718df665fb7e5ed800186b38fc904362557ad3c25d5be69de503cce030/src/bst_plugins_experimental/sources/git_tag.py", line 939, in track
        self.mirror.ensure_trackable()
      File "/var/home/adrian/Projects/build-meta/.bst/staged-junctions/junctions/bst-plugins-experimental.bst/7a4409718df665fb7e5ed800186b38fc904362557ad3c25d5be69de503cce030/src/bst_plugins_experimental/sources/git_tag.py", line 334, in ensure_trackable
        self.source.call(
      File "/usr/local/lib64/python3.11/site-packages/buildstream/plugin.py", line 728, in call
        exit_code, _ = self.__call(
                       ^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/plugin.py", line 950, in __call
        exit_code, output = utils._call(args, cwd=cwd, env=env, stdin=stdin, stdout=stdout, stderr=stderr)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/buildstream/utils.py", line 1435, in _call
        with _signals.suspendable(suspend_proc, resume_proc), _signals.terminator(kill_proc), subprocess.Popen(
      File "/usr/lib64/python3.11/contextlib.py", line 155, in __exit__
        self.gen.throw(typ, value, traceback)
      File "/usr/local/lib64/python3.11/site-packages/buildstream/_signals.py", line 113, in terminator
        terminate_func()
      File "/usr/local/lib64/python3.11/site-packages/buildstream/utils.py", line 1423, in kill_proc
        _kill_process_tree(process.pid)
      File "/usr/local/lib64/python3.11/site-packages/buildstream/utils.py", line 1342, in _kill_process_tree
        proc = psutil.Process(pid)
               ^^^^^^^^^^^^^^^^^^^
      File "/usr/local/lib64/python3.11/site-packages/psutil/__init__.py", line 332, in __init__
        self._init(pid)
      File "/usr/local/lib64/python3.11/site-packages/psutil/__init__.py", line 373, in _init
        raise NoSuchProcess(pid, msg='process PID not found')
    psutil.NoSuchProcess: process PID not found (pid=2463427)
```