Fix CI

[corranwebster]

This gets a reasonable baseline CI working for Kiva and Enable. It covers Python 3.8 and 3.10 with a reasonable set of Kiva backends and ETS toolkits. It splits out the Linux Qt dependency installation into a separate action as is done in other ETS projects so it can be re-used across workflows.

There are a number of test cases skipped:

• WxPython on MacOS and Linux due to lack of appropriate wheels
• PyQt5 on Python 3.10 due to #1037
• PyQt5 on Windows due to #1038

This also adds a skip to a Cairo backend test case due to #1035 and a couple of drive-by fixes to the Cairo Kiva backend (Cairo was previously not being tested).

[corranwebster]

For reviewer: run of bleeding edge tests against this branch. https://github.com/enthought/enable/actions/runs/4731925723