[packaging][CI/CD] Build wheels from sdist

[webknjaz]

Basically, https://github.com/libgit2/pygit2/blob/885553b6468e71efcdd333fbfef8651b30729187/.github/workflows/wheels.yml needs to be updated to have all wheel-building jobs depend on the sdist one. And cibuildwheel, when called, should get a path to the .tar.gz file instead of the Git checkout. This will make sure the process pip install would use when it hits a need to build from sdist does actually work.