gh-77377: Ensure multiprocessing SemLock is valid for spawn-based Process before serializing it (#107275)

Ensure multiprocessing SemLock is valid for spawn Process before serializing it.

Creating a multiprocessing SemLock with a fork context, and then trying to pass it to a spawn-created Process, would segfault if not detected early.

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Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Antoine Pitrou <pitrou@free.fr>