Fix type hint

Author: benoit74

src/zimscraperlib/inputs.py

@@ -16,7 +16,7 @@
 def handle_user_provided_file(
     source: Optional[Union[pathlib.Path, str]] = None,
     dest: Optional[pathlib.Path] = None,
-    in_dir: pathlib.Path = None,
+    in_dir: Optional[pathlib.Path] = None,
     nocopy: bool = False,
 ) -> Union[pathlib.Path, None]:
     """path to downloaded or copied a user provided file (URL or path)