Don't set stacklevel bc of multiple entrypoints

Author: jseabold

pandas/core/groupby/grouper.py

@@ -494,7 +494,7 @@ def __init__(
             elif is_categorical_dtype(self.grouper):
 
                 if observed is None:
-                    warnings.warn(_observed_msg, FutureWarning, stacklevel=5)
+                    warnings.warn(_observed_msg, FutureWarning)
                     observed = False
 
                 self.grouper, self.all_grouper = recode_for_groupby(