Also fixed virtualenv install under 2.7

* Make compatible with pip 22.2+, restoring Requires-Python functionality there.

Fixes https://github.com/buildout/buildout/issues/613.

Note: we are patching `process_url` from `setuptools`.
The existing comment says that this method was copied over from setuptools 46.1.3.
I was wondering, so I checked: the method is still the same in latest setuptools.  And it is largely unchanged since setuptools 42.0.2.
So for that part we should still be compatible with quite a long range of setuptools versions.

* process_url patch: must pass cache_link_parsing=False.

This fixes test failures: extdemo-1.5 was not found, because the previous index page containing only extdemo-1.4 was cached.
We were passing this before to HTMLPage, and still do as a fallback, but I missed that this was also needed in pip 22.2+ for the new IndexContent class.

Add support for python311-315 in conditional section expressions. [master]

Prevent running gh-actions twice for push/pull.

Copied from the zopefoundation repositories.
See https://github.com/zopefoundation/meta/issues/145
and the final version at https://github.com/zopefoundation/meta/blob/9c24f7380973de989c5132ec9f28fa71f1397f20/config/c-code/tests.yml.j2#L93

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Solution: remove it now that it seems to be correct

Solution: ignore until fixable

Solution: be explicit instead of relying on auto-discovery

Solution: workaround pip _distutils_hack

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Solution: fix it

btw, exclude CI only file from sdist

Solution: use explicit strings

Solution: update

Solution: stop testing it

Solution: be explicit where to find it

Solution: rewrite in easy_install

Keep compatible with earlier pip versions.
Fixes https://github.com/buildout/buildout/issues/598

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Solution: use `python -m pip`

Solution: implement and document it

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Solution: check value explicitely and open corresponding files

Solution: check for existence of namespace directories