Update series.pyi, tackling issue pandas-dev#1101

Imported Index from pandas
and
Changed keys method:
def keys(self) -> Index: ...

Author: janlodewijk

pandas-stubs/core/series.pyi

@@ -34,6 +34,7 @@ from pandas import (
     PeriodDtype,
     Timedelta,
     Timestamp,
+    Index,
 )
 from pandas.core.api import (
     Int8Dtype as Int8Dtype,
@@ -652,7 +653,7 @@ class Series(IndexOpsMixin[S1], NDFrame):
     ) -> _str: ...
     def to_xarray(self) -> xr.DataArray: ...
     def items(self) -> Iterable[tuple[Hashable, S1]]: ...
-    def keys(self) -> list: ...
+    def keys(self) -> Index: ...
     @overload
     def to_dict(self, *, into: type[dict] = ...) -> dict[Any, S1]: ...
     @overload