Help tools know the type of a Commit's parents

mypy seems not to need this, and already infers the specific type
List[Commit], but some other type checkers -- at least pylance, and
thus probably also pyright -- do not infer this.

Author: EliahKagan

git/objects/commit.py

@@ -753,7 +753,7 @@ def _deserialize(self, stream: BytesIO) -> "Commit":
         readline = stream.readline
         self.tree = Tree(self.repo, hex_to_bin(readline().split()[1]), Tree.tree_id << 12, "")
 
-        self.parents = []
+        self.parents = []  # type: List[Commit]
         next_line = None
         while True:
             parent_line = readline()