Workflow to alert us to make a new PyPI release

It's easy to forget when merging some PR needs a new PyPI release of the library. See #9825 for the latest example; there have been several in recent times.

We should probably have some action that alerts us to this automatically. It could trigger on pushes to master, test `.load_all()` with the latest PyPI release, and do something if this causes an error.

"Do something" could be
- Create an issue prompting us to create a new release.
- Directly prepare a new release and create a PR, so we just need to approve and merge (... less work, but also less control)

No specific files or tests are named; begin by inspecting the repository’s master-branch CI/release workflow configuration and any packaging/release scripts. Identify where `.load_all()` runs today, then plan where to add a check against the latest PyPI release in that path. Run the relevant workflow/job to validate behavior, and consider it done when master pushes automatically generate a release alert (issue or PR) on failure.

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