Sometimes, an imprecise branch reference can't be resolved during continuation

[webknjaz]

I've hit a conflict, fixed it re-ran cherry-picker with --continue and got a traceback + an invalid state in the config:

$ uvx --from cherry-picker cherry_picker --continue
🐍 🍒 ⛏
Traceback (most recent call last):
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/bin/cherry_picker", line 10, in <module>
    sys.exit(cherry_pick_cli())
             ~~~~~~~~~~~~~~~^^
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/click/core.py", line 1161, in __call__
    return self.main(*args, **kwargs)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/click/core.py", line 1082, in main
    rv = self.invoke(ctx)
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/click/core.py", line 1443, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/click/core.py", line 788, in invoke
    return __callback(*args, **kwargs)
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/click/decorators.py", line 33, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/cherry_picker/cherry_picker.py", line 855, in cherry_pick_cli
    cherry_picker.continue_cherry_pick()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/cherry_picker/cherry_picker.py", line 639, in continue_cherry_pick
    commits = get_commits_from_backport_branch(base)
  File "~/.cache/uv/archive-v0/EI4uSp-Fsr1kEx0L58PRM/lib/python3.13/site-packages/cherry_picker/cherry_picker.py", line 965, in get_commits_from_backport_branch
    output = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
  File "~/.pyenv/versions/3.13.0/lib/python3.13/subprocess.py", line 472, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
           ~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
               **kwargs).stdout
               ^^^^^^^^^
  File "~/.pyenv/versions/3.13.0/lib/python3.13/subprocess.py", line 577, in run
    raise CalledProcessError(retcode, process.args,
                             output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['git', 'log', '--format=%H', 'stable-2.14..']' returned non-zero exit status 128.

$ uvx --from cherry-picker cherry_picker --continue
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Run state cherry-picker.state=CONTINUATION_STARTED in Git config is not known.
Perhaps it has been set by a newer version of cherry-picker. Try upgrading.
Valid states are: BACKPORT_PAUSED, UNSET. If this looks suspicious, raise an issue at https://github.com/python/cherry-picker/issues/new.
As the last resort you can reset the runtime state stored in Git config using the following command: `git config --local --remove-section cherry-picker`

Running that Git command revealed the inability of Git to resolve the stable-2.14 reference, while it is perfectly fine resolving the remote pointer origin/stable-2.14:

$ git log --format='%H' stable-2.14..
fatal: ambiguous argument 'stable-2.14..': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

$ git log --format='%H' stable-2.14.. --
fatal: bad revision 'stable-2.14..'

$ git log --format='%H' origin/stable-2.14..

This seems to be easily fixable by passing a better identifier to get_commits_from_backport_branch().