Potential fix for pull request finding 'Explicit returns mixed with implicit (fall through) returns'

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

Author: mhucka

src/openfermion/chem/pubchem_test.py

@@ -83,6 +83,7 @@ def _get_geometry_with_retries(self, name):
                 if attempt == max_retries - 1:
                     raise
                 time.sleep(delay)
+        return None
 
     @patch('pubchempy.get_compounds', mock_get_compounds)
     def test_water(self):