https://github.com/pypa/packaging/issues/678

Nightly builds were failing because newer setuptools didn't like the
Python version number:

```
% .tox/anypy/bin/python -c "import pkg_resources as p; p.load_entry_point('coverage', 'console_scripts', 'coverage')()"
Traceback (most recent call last):
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2711, in _dep_map
    return self.__dep_map
           ^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2826, in __getattr__
    raise AttributeError(attr)
AttributeError: _Distribution__dep_map

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 522, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2855, in load_entry_point
    return ep.load()
           ^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2467, in load
    self.require(*args, **kwargs)
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2489, in require
    reqs = self.dist.requires(self.extras)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2746, in requires
    dm = self._dep_map
         ^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2713, in _dep_map
    self.__dep_map = self._filter_extras(self._build_dep_map())
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 2728, in _filter_extras
    invalid_marker(marker) or not evaluate_marker(marker)
    ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 1415, in invalid_marker
    evaluate_marker(text)
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/__init__.py", line 1433, in evaluate_marker
    return marker.evaluate()
           ^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/_vendor/packaging/markers.py", line 245, in evaluate
    return _evaluate_markers(self._markers, current_environment)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/_vendor/packaging/markers.py", line 151, in _evaluate_markers
    groups[-1].append(_eval_op(lhs_value, op, rhs_value))
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/_vendor/packaging/markers.py", line 109, in _eval_op
    return spec.contains(lhs, prereleases=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/_vendor/packaging/specifiers.py", line 565, in contains
    normalized_item = _coerce_version(item)
                      ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/_vendor/packaging/specifiers.py", line 36, in _coerce_version
    version = Version(version)
              ^^^^^^^^^^^^^^^^
  File "/Users/nedbatchelder/coverage/trunk/.tox/anypy/lib/python3.12/site-packages/pkg_resources/_vendor/packaging/version.py", line 197, in __init__
    raise InvalidVersion(f"Invalid version: '{version}'")
pkg_resources.extern.packaging.version.InvalidVersion: Invalid version: '3.12.0a5+'
```