[chore] Add CI step to check that Python codegen files are up to date #5680

Currently there's no check in the CI to verify that the files generated by the codegen script (which are the contents of plotly/graph_objs/) are up-to-date after the source files used in the codegen process are changed (primarily the files in codegen/ itself, but for example basevalidators.py is also used).

This means that the CI can be green even if the generated files are out of date. This happened recently with #5673 resulting in the follow-up PR #5679.

We should add a CI job that runs the codegen and then fails if the generated files do not match what's committed in the repo.