I don't have a complete fix for#2004 yet, but since it's confirmed to fail on the main branch of this upstream repository (mentioned in#1988 (comment), though not due to#1988), I figured my partial fix might be worth putting into place. With these changes, the problem in the Cygwin test job turns from being unable to run any tests to being able to run all the tests but with one new failure compared to the way it was before#2004 (i.e. with one non-xfail failure).

This uses the officialpip bootstrap scripthttps://bootstrap.pypa.io/get-pip.py to installpip in the virtual environment. This allows the actual installation of GitPython and its dependencies, including all test dependencies, to complete without problems. Aside from tests that are expected to fail and are already marked xfail, all tests passexcept fortest_installation, which fails for the same reason. It presumably would also pass if the bootstrap script were used there too, but I believe the current intent of that test is to verify that installation succeeds when done in an ordinary way.

I am likewise reluctant to marktest_installation as xfail on Cygwin, unless that turns out to be truly necessary, because none of this happens on my local Cygwin environment on a Windows 10 development machine. It seems like it is triggered by some combination of changing packages and something wrong or otherwise specific about the Cygwin workflow.

This PR includes some changes to the workflow that are not actually necessary for the workaround it confers. The changes thatare needed are:

• Refraining from havingvenv automatically attempt to installpip.
• Installingpip in the virtual environment explicitly using the bootstrap script.
• Installing thewget Cygwin package to download the bootstrap script without extra complexity or risking encoding/line-ending mismatches.

All the rest is to make the workflow run a little faster, andmaybe be slightly more robust in ways that are not relevant to#2004 and not very important. The most significant of them is switching back to the Cygwin installation action we had previously been using, which is less configurable (it does not support installing Cygwin packages at specific versions, which we had needed to do at one time), but which is faster because it does not first have to install Chocolatey to use it as an intermediary for installing Cygwin.

I kept those changes here because I think it's easier to iterate on this if it is left in. But if you'd like I'd be pleased to undo the nonessential changes, which can always be brought back later and separately. I have tested in7fd5f15 to make sure that this really works, so undoing those changes could be as simple as adding that one commit.