fix(types): cr_frame may be None

Author: ashm-dev

stdlib/types.pyi

@@ -463,7 +463,7 @@ class CoroutineType(Coroutine[_YieldT_co, _SendT_nd_contra, _ReturnT_nd_co]):
     @property
     def cr_code(self) -> CodeType: ...
     @property
-    def cr_frame(self) -> FrameType: ...
+    def cr_frame(self) -> FrameType | None: ...
     @property
     def cr_running(self) -> bool: ...
     @property