Extend PyPI test workflow to wheels

[mdickinson]

We already have a cron-based workflow test-from-pypi.yml that checks that the Traits tests pass with all the latest packages from PyPI; that workflow installs from the PyPI sdist.

This PR extends that workflow to also test wheels.

The goal is for Traits users not to need to compile anything; for that reason, we attempt to ensure that everything is installed from wheels by using the --only-binary flag to pip. We may need to relax this requirement if some of the test dependencies don't have wheels available (NumPy would be the most likely candidate for this).

EDIT: we're not using --only-binary :all:, since that would require that Pyface and TraitsUI have wheels available.

I'll temporarily adjust the trigger for this PR to be on pull request, so that we can verify that it works. Then I'll put the cron trigger back before merging.

[mdickinson]

Ah, of course - we don't have wheels for Pyface or TraitsUI. I guess I really want something weaker than --only-binary that says it's okay to install from sdist for pure Python packages.

I'll remove the :all: specifier from the --only-binary option.

[rahulporuri]

Ah, of course - we don't have wheels for Pyface or TraitsUI. I guess I really want something weaker than --only-binary that says it's okay to install from sdist for pure Python packages.

It should be trivial to replicate this for almost all of ETS - which should reduce one more manual step involved in the release process.

[rahulporuri]

LGTM.

[mdickinson]

It should be trivial to replicate this for almost all of ETS

It's probably worth it for the simpler pure-Python cases: TraitsUI, Pyface, Apptools, Envisage. (And of course in those cases we only need a single wheel, not 20.)

Enable and Chaco may be more troublesome. Mayavi wheels are a can of worms with respect to VTK versions.

[rahulporuri]

i've created an umbrella issue in the ets repository - enthought/ets#56

[mdickinson]

@rahulporuri Thanks for the review.