bugfix: fix incorrect path slice in strict module loader

Summary:
`path[:12]` takes the first 12 characters of the path instead of stripping
`__init__.py` from the end. This meant `submodule_search_locations` for strict
packages would always be wrong. Replaced with `os.path.dirname(path)` which is
the standard idiom for getting the directory of a file.

Reviewed By: yoney

Differential Revision: D97805946

fbshipit-source-id: 55df9a1b93969b921348661a937919575c74f692

Author: alexmalyshev

cinderx/PythonLib/cinderx/compiler/strict/loader.py

@@ -543,7 +543,7 @@ def source_to_code(
             # containing the "__init__.py").
             submodule_search_locations = None
             if path.endswith("__init__.py"):
-                submodule_search_locations = [path[:12]]
+                submodule_search_locations = [os.path.dirname(path)]
             # Usually _optimize will be -1 (which means "default to the value
             # of sys.flags.optimize"). But this default happens very deep in
             # Python's compiler (in PyAST_CompileObject), so if we just pass