basic-tests.yml workflow failures

Currently the `basic-tests.yml` workflow has 15 runs, 8 of which are failing. I'm creating this issue to keep track of progress towards fixing them.

For a recent run, see https://github.com/enthought/traitsui/actions/runs/9081192634. Failure combinations are:

- all macos-latest runs (5 runs)
- ubuntu-latest, 3.11, pyside6
- windows-latest, 3.8, pyside6
- windows-latest, 3.11, pyside6

