fix: gi_yieldfrom can be any iterator type being yielded from (#14334)

Author: bzoracler

stdlib/types.pyi

@@ -388,7 +388,7 @@ class GeneratorType(Generator[_YieldT_co, _SendT_contra, _ReturnT_co]):
     @property
     def gi_running(self) -> bool: ...
     @property
-    def gi_yieldfrom(self) -> GeneratorType[_YieldT_co, _SendT_contra, Any] | None: ...
+    def gi_yieldfrom(self) -> Iterator[_YieldT_co] | None: ...
     if sys.version_info >= (3, 11):
         @property
         def gi_suspended(self) -> bool: ...