Fix forward ref

Author: Yobmod

git/objects/util.py

@@ -37,7 +37,7 @@
 T_TIobj = TypeVar('T_TIobj', bound='TraversableIterableObj')   # for TraversableIterableObj.traverse()
 
 TraversedTup = Union[Tuple[Union['Traversable', None], 'Traversable'],  # for commit, submodule
-                     TraversedTreeTup]                                   # for tree.traverse()
+                     'TraversedTreeTup']                                   # for tree.traverse()
 
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