Update build machinery to support Python 3.8 and PySide 6

mdickinson commented 2 years ago

This PR extends the build machinery to support Python 3.8 and PySide 6, and does general cleanup and streamlining of the GitHub Actions workflows.

Notable changes:

I've added a minimal pyproject.toml file.
For EDM-based workflows, we use the GitHub Actions Python for our bootstrap environment instead of creating an EDM bootstrap environment; creation and population of the bootstrap environment takes ~5s.
For the wxPython workflow, I've disabled Python 3.6: the workflow only runs on Python 3.8. The pip install of wxPython 4.2.0 on Python 3.6 appears to be broken.
I've added platform-specific skips for a couple of troublesome tests; there are linked issues for those skips
All workflows can now be run manually

mdickinson commented 2 years ago

Marking as draft: I'm aiming to combine this with general build system updates.

mdickinson commented 2 years ago

Thanks. Updating branch protections so that I can merge.

enthought / envisage