Add __or__ to defaultdict

Author: eltoder

stdlib/collections/__init__.pyi

@@ -391,6 +391,9 @@ class defaultdict(dict[_KT, _VT], Generic[_KT, _VT]):
     def __missing__(self, __key: _KT) -> _VT: ...
     def __copy__(self) -> Self: ...
     def copy(self) -> Self: ...
+    if sys.version_info >= (3, 9):
+        def __or__(self, other: Mapping[_T1, _T2]) -> defaultdict[_KT | _T1, _VT | _T2]: ...
+        def __ror__(self, other: Mapping[_T1, _T2]) -> defaultdict[_KT | _T1, _VT | _T2]: ...
 
 class ChainMap(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     maps: list[MutableMapping[_KT, _VT]]