When Blender started with an extension enabled from a repository that
referenced a directory that didn't exist - creating the directory
and extensions would fail to import the extension.
This happened because the missing state of the module was cached.
Resolve by clearing Python's path cache for the repository after
running install actions which may have created the directory.
Also run importlib.invalidate_caches() when manually refreshing local
extensions to ensure modules cached as missing can be imported if
they have become available.
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