Update importlib cache,source return types to StrPath (#13509)

This has been true since Python 3.6.

Author: ichard26

stdlib/_frozen_importlib_external.pyi

@@ -26,8 +26,8 @@ else:
 
 MAGIC_NUMBER: bytes
 
-def cache_from_source(path: str, debug_override: bool | None = None, *, optimization: Any | None = None) -> str: ...
-def source_from_cache(path: str) -> str: ...
+def cache_from_source(path: StrPath, debug_override: bool | None = None, *, optimization: Any | None = None) -> str: ...
+def source_from_cache(path: StrPath) -> str: ...
 def decode_source(source_bytes: ReadableBuffer) -> str: ...
 def spec_from_file_location(
     name: str,