CI: fail with warnings, and several minor tunings to test workflow

[mwtoews]

Notes on the changes:

• Tests will fail from warnings (-Werror)
• Use verbose messages with pytest, since this is the primary output to review
• Change fail-fast: false to run all jobs of a matrix, even if there is one failure
• Remove the pre-commit workflow job, since pre-commit.ci was recently configured
• Use conda to install pytest for the conda jobs (not pip)
• Apt should't install python3-pip, and use apt-get for non-interactive use
• Remove 'paths' for 'push', so that the tests are re-run after pull-requests are merged to master

[EwoutH]

Looks good!

[EwoutH]

I don't understand what's happening here fully, I would make sure to test this.

[mwtoews]

The -${{ strategy.job-index }} was an necessary number for the artefact name, e.g. "cibw-wheels-macos-latest-2.zip". So now it becomes just "cibw-wheels-macos-latest.zip". Artefacts can be viewed/downloaded in the GHA Summary, which I sometimes download to inspect or upload to PyPI (hopefully less-so for future releases).

[EwoutH]

Doesn't this give a problem with macOS artifact names? Since cibuildwheel runs both on x86 and Arm runners?

Edit: Nevermind, they already merge them on the cibuildwheel end to a single artifact, so this doesn't change anything.

[mwtoews]

I just checked to see, and the files look good. Each artefact contains several wheel files created from the runner, so there's no conflict.