BUG: Prevent pd.Series.groupby from showing FutureWarning (#60894)

Call is_in_obj only when obj is a DataFrame at get_grouper()

Author: sanggon6107

pandas/core/groupby/grouper.py

@@ -1023,7 +1023,7 @@ def is_in_obj(gpr) -> bool:
             return False
 
     for gpr, level in zip(keys, levels):
-        if is_in_obj(gpr):  # df.groupby(df['name'])
+        if isinstance(obj, DataFrame) and is_in_obj(gpr):  # df.groupby(df['name'])
             in_axis = True
             exclusions.add(gpr.name)