Remove trailing whitespaces

Author: githubalexliu

pandas/core/groupby/groupby.py

@@ -2661,7 +2661,7 @@ def sem(self, ddof: int = 1, numeric_only: bool = False) -> NDFrameT:
         See Also
         --------
         Series.sem : Return unbiased standard error of the mean over requested axis.
-        DataFrame.sem : Return unbiased standard error of the mean over requested axis.      
+        DataFrame.sem : Return unbiased standard error of the mean over requested axis.
 
         Examples
         --------