GeezerVison

- In the Cygwin CI workflow, move `runs-on` below `strategy`, for
  greater consistency with other workflows.

- In the Cygwin CI jobs, use `pwsh` rather than `bash` for the
  `git config` command run outside of Cygwin, since `pwsh` is the
  default shell for such commands, it's the shell the Cygwin setup
  action uses, and it avoids creating the wrong impression that
  `bash` is needed.

- Use "virtual environment" instead of "virtualenv" in some step
  names to avoid possible confusion with the `virtualenv` pacakge.

- Remove comments in the PyPA package upgrade steps, which are
  more self-documenting since 727f4e9 (gitpython-developers#2043).

This installs the `python-pip-wheel`, `python-setuptools-wheel`,
and `python-wheel-wheel` packages on Cygwini CI, which provide
`.whl` files for `pip`, `setuptools`, and `wheel`.

By making those wheels available, this fixes gitpython-developers#2004 better than the
previous workaround, allowing `ensurepip` to run without the error:

    Traceback (most recent call last):
      File "/usr/lib/python3.9/runpy.py", line 188, in _run_module_as_main
        mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
      File "/usr/lib/python3.9/runpy.py", line 147, in _get_module_details
        return _get_module_details(pkg_main_name, error)
      File "/usr/lib/python3.9/runpy.py", line 111, in _get_module_details
        __import__(pkg_name)
      File "/usr/lib/python3.9/ensurepip/__init__.py", line [30](https://github.com/EliahKagan/GitPython/actions/runs/13454947366/job/37596811693#step:10:31), in <module>
        _SETUPTOOLS_VERSION = _get_most_recent_wheel_version("setuptools")
      File "/usr/lib/python3.9/ensurepip/__init__.py", line 27, in _get_most_recent_wheel_version
        return str(max(_wheels[pkg], key=distutils.version.LooseVersion))
    ValueError: max() arg is an empty sequence

This change takes the place of the main changes in gitpython-developers#2007 and gitpython-developers#2009.
In particular, it should allow `test_installation` to pass again.

This also delists non-wheel Cygwin packages such as `python39-pip`,
which are not needed (or at least no longer needed).

(The python-{pip,setuptools,wheel}-wheel packages are, as their
names suggest, intentionally not specific to Python 3.9. However,
this technique will not necessarily carry over to Python 3.12,
depending on what versions are supplied and other factors. This may
be relevant when another attempt like gitpython-developers#1988 is made to test/support
Python 3.12 on Cygwin. At least for now, though, this seems
worthwhile for fixing the Cygwin 3.9 environment, making it more
similar to working local Cygwin environments and letting the
workflow be more usable as guidance to how to set up a local Cygwin
environment for GitPython development, and letting the installation
test pass automatically.)