61734: Add mutex around module dirs cache cleanup

[afischer-opentext-com]

What does this PR do?

What issues does this PR fix or reference?

Fixes: #61734

Previous Behavior

There was no mutex around code cleaning up the sys.path and a local variable caching module paths.

New Behavior

There is a mutex around code cleaning up the sys.path and a local variable caching module paths. This shall prevent prevent the issues mentioned in the related issue #61734

Remove this section if not relevant

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• [ ] Docs
• [ ] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [ ] Tests written/updated

Commits signed with GPG?

Yes