Python wheel workflow should validate sdist

The python wheel workflow should have a validation step that does a `pip install` of the wheel, including a `pip install --no-binary` to verify the build-from-source actually works.

Start by locating the Python wheel workflow and reviewing how it builds wheel and source distributions. Run the workflow, then verify that the wheel installs normally and that a pip install --no-binary build-from-source path succeeds; done means both validation paths pass in CI.

Written by the indexing model from the issue text.