style: fix trailing blank line in gb.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: iamDecode

sklearn_pmml_model/ensemble/gb.py

@@ -274,4 +274,3 @@ def _more_tags(self):
     if hasattr(GradientBoostingRegressor, '_more_tags'):
       return GradientBoostingRegressor._more_tags(self)
     return {}
-