Error when building `plasmapy_sphinx`'s documentation

[namurphy]

The documentation builds for CI in #22 ended up getting the following error. I haven't looked into it, but seems related to setuptools_scm and how the version is being set. This looks unrelated to #23.

      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/sphinx/config.py", line 611, in eval_config_file
        raise ConfigError(msg % traceback.format_exc()) from exc
    sphinx.errors.ConfigError: There is a programmable error in your configuration file:
    
    Traceback (most recent call last):
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/importlib/metadata/__init__.py", line 407, in from_name
        return next(iter(cls.discover(name=name)))
    StopIteration
    
    During handling of the above exception, another exception occurred:
    
    Traceback (most recent call last):
      File "/home/runner/work/plasmapy_sphinx/plasmapy_sphinx/plasmapy_sphinx/__init__.py", line 91, in <module>
        __version__ = version("plasmapy_sphinx")
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/importlib/metadata/__init__.py", line 987, in version
        return distribution(distribution_name).version
               ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/importlib/metadata/__init__.py", line 960, in distribution
        return Distribution.from_name(distribution_name)
               ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/importlib/metadata/__init__.py", line 409, in from_name
        raise PackageNotFoundError(name)
    importlib.metadata.PackageNotFoundError: No package metadata was found for plasmapy_sphinx
    
    During handling of the above exception, another exception occurred:
    
    Traceback (most recent call last):
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/sphinx/config.py", line 596, in eval_config_file
        exec(code, namespace)  # NoQA: S102
        ~~~~^^^^^^^^^^^^^^^^^
      File "/home/runner/work/plasmapy_sphinx/plasmapy_sphinx/docs/conf.py", line 28, in <module>
        from plasmapy_sphinx import __version__ as release
      File "/home/runner/work/plasmapy_sphinx/plasmapy_sphinx/plasmapy_sphinx/__init__.py", line 100, in <module>
        __version__ = get_version(
            root="..", relative_to=__file__, fallback_version=fallback_version
        )
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/_get_version_impl.py", line 235, in get_version
        maybe_version = _get_version(config, force_write_version_files=True)
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/_get_version_impl.py", line 105, in _get_version
        parsed_version = parse_version(config)
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/_get_version_impl.py", line 63, in parse_version
        or parse_scm_version(config)
           ~~~~~~~~~~~~~~~~~^^^^^^^^
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/_get_version_impl.py", line 41, in parse_scm_version
        return _entrypoints.version_from_entrypoint(
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
            config,
            ^^^^^^^
            entrypoint="setuptools_scm.parse_scm",
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            root=config.absolute_root,
            ^^^^^^^^^^^^^^^^^^^^^^^^^^
        )
        ^
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/_entrypoints.py", line 56, in version_from_entrypoint
        maybe_version: version.ScmVersion | None = fn(root, config=config)
                                                   ~~^^^^^^^^^^^^^^^^^^^^^
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/git.py", line 319, in parse
        return _git_parse_inner(
            config, wd, describe_command=describe_command, pre_parse=effective_pre_parse
        )
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/setuptools_scm/git.py", line 365, in _git_parse_inner
        tag = config.version_cls(config.fallback_version or "0.0")
      File "/opt/hostedtoolcache/Python/3.13.11/x64/lib/python3.13/site-packages/packaging/version.py", line 202, in __init__
        raise InvalidVersion(f"Invalid version: {version!r}")
    packaging.version.InvalidVersion: Invalid version: 'unknown'