Python 3.7 is not supported on GitHub Actions ubuntu-latest runner:
https://github.com/actions/setup-python/issues/962
Python 3.7 has reached EOL more than 1 year ago anyway,
so not worth the effort supporting it.
To preview the docs, run:
```
scripts/build-python-docs.sh
firefox dist/html/index.html
```
I have removed the Makefile because modern Sphinx Makefile is just a
wrapper for `sphinx-build -M`:
3596590317/sphinx/templates/quickstart/Makefile.new_t
and sphinx-quickstart even has an option `--no-makefile`.
`make.bat` makes even less sense.
In `scripts/build-python-docs.sh` I use `sphinx-build` directly
without `make` wrapper.
We install `tox` via `pipx` in `Dockerfile`, there is no need to
configure path to `python3.7`.
Also remove use of `pushd`/`popd` and switch from `bash` to `/bin/sh`.
musllinux images miss PyPy interpreters,
we want to skip building PyPy wheels for musl
instead of failing the build.
Also remove workaround from CI scripts.