complete typing in BaseGroupBy (#1439)

Author: MarcoGorelli

pandas-stubs/core/groupby/groupby.pyi

@@ -373,7 +373,7 @@ class BaseGroupBy(SelectionMixin[NDFrameT], GroupByIndexingMixin):
         **kwargs: Any,
     ) -> T: ...
     @final
-    def get_group(self, name) -> NDFrameT: ...
+    def get_group(self, name: Hashable) -> NDFrameT: ...
     @final
     def __iter__(self) -> Iterator[tuple[Hashable, NDFrameT]]: ...
     @overload