Add remaining types to IndexFile ._preprocess_add_items() to .diff()

Author: Yobmod

git/index/base.py

@@ -586,7 +586,8 @@ def _to_relative_path(self, path: PathLike) -> PathLike:
             raise ValueError("Absolute path %r is not in git repository at %r" % (path, self.repo.working_tree_dir))
         return os.path.relpath(path, self.repo.working_tree_dir)
 
-    def _preprocess_add_items(self, items):
+    def _preprocess_add_items(self, items: Sequence[Union[PathLike, Blob, BaseIndexEntry, Submodule]]
+                              ) -> Tuple[List[PathLike], List[BaseIndexEntry]]:
         """ Split the items into two lists of path strings and BaseEntries. """
         paths = []
         entries = []