Add missing SeriesGroupBy.sum

Author: danielroseman

pandas-stubs/core/groupby/generic.pyi

@@ -100,6 +100,7 @@ class SeriesGroupBy(GroupBy):
     def nlargest(self, n: int = ..., keep: str = ...) -> Series[S1]: ...
     def nsmallest(self, n: int = ..., keep: str = ...) -> Series[S1]: ...
     def nth(self, n: int | Sequence[int], dropna: str | None = ...) -> Series[S1]: ...
+    def sum(self) -> Series[S1]: ...
 
 class _DataFrameGroupByScalar(DataFrameGroupBy):
     def __iter__(self) -> Iterator[tuple[Scalar, DataFrame]]: ...