Requested for the _imagingtk fix.

I think this is how specifying the shell works.  The documentation
isn't terribly clear.

For some reason wheel wasn't installed properly.

setup.py bdist_wheel goes to dist/*.whl
pip wheel goes to *.whl

I'm using selftest.py to check whether I've installed everything.
Pytest actually finds and runs the tests.  For some reason that wasn't
running earlier.

Upload coverage information, add Cygwin to the list of systems with CI,
space out entries.

The actual test step wasn't running, so try to run that as a shell
script rather than an executable.  Also get more of the dependencies
installed.

The old bash downloader will be removed soon.

Cygwin is trying to use the highest-available Python version.
One of the Python packages has scripts in /usr/bin that should be in the python39- subpackage.

They segfault in one of the NumPy tests, but they run.

Segfaults are annoying to debug.

From a suggestion on the PR, make it clearer that Cygwin runs on
Windows.  Also record the Cygwin versions in the check against Python
versions.

CI: Add a Cygwin run to GitHub Actions

There are still a few things that are weird, but this looks much better than what I have now.

Some early runs needed to explicitly specify the minor version to avoid calling python3.9 which had none of the dependencies installed.
That problem should be fixed.

As suggested by code review.

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Only install NumPy through pip on 64-bit.

Thanks for catching that, I'd forgotten the NumPy 1.21 problems were only on 64-bit.

Copied from the MIT-licensed:
https://github.com/actions/cache/blob/main/examples.md#using-pip-to-get-cache-location

This might pave the way for caching the Cygwin install, which might speed things up a bit.

Allows me to avoid .ci/build_cygwin.sh

Avoid pip warnings.

This may be a problem with using a login shell (starts in ~) rather than with using bash over dash.  We'll see in a bit.

I should probably avoid login shells in any step that uses a relative path.

Hopefully this makes sure rebase finds all of pillow's C extension modules so rebase failures are less likely.

Do not install NumPy on Python 3.11

So that's how I was supposed to resolve that merge conflict.  Thank you.

Finish the last few of these.  It's usually unnecessary, but I ran into trouble once with NumPy, and will likely run into more problems if I start submitting packages.

A different option would be to use alternatives to point python3 at the right python.

* CI: Update Cygwin pip, but not on 32-bit

32-bit Cygwin pip>=22 fails to install coverage.

* CI: Let .ci/install.sh handle updating pip

* CI Combine pip update conditions

* CI: Don't try to upgrade pip on 32-bit Cygwin

* CI: Use alternatives to select python version

* CI: Specify full path to alternatives

/usr/sbin isn't in PATH

* DBG: Print uname to try to avoid bad pip install.

pip>=22 on 32-bit Cygwin seems to cause problems installing coverage.  I have no idea why this is, so I just skip upgrading pip there.

* FIX: Fix syntax of conditional for 32-bit Cygwin

I have no idea if it needs to be able to accept i386, but it will if it comes up.

* FIX: Revert earlier debug change.

Cygwin recommends using 64-bit if at all possible, and will discontinue support entirely within the next year or so.  

This also reduces CI load, which I suppose is polite to those who provide it at no cost.

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Install seems to be working now.

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Removed steps that are currently unnecessary.  Hopefully they stay that way.

Added Cygwin badge

Let's see if this works.

Co-authored-by: Ondrej Baranovič <nulano@nulano.eu>