SIENTIAPDE-2226: Assign DataFrame before pytest.raises in test

- Build the DataFrame outside the `pytest.raises` block so only the
  call under test can raise the expected ValueError.

tests/utils/repository/test_data_manager_repository.py

@@ -134,8 +134,9 @@ def test_set_timezone_on_index_converts_aware_index_to_utc():
 
 def test_set_timezone_on_index_non_datetime_index_raises():
     repo = dmr.DataManagerRepository(MagicMock())
+    df = pd.DataFrame({'v1': [1]})
     with pytest.raises(ValueError, match='Index is not a DatetimeIndex'):
-        repo._set_timezone_on_index(pd.DataFrame({'v1': [1]}))
+        repo._set_timezone_on_index(df)
 
 
 def test_prepare_training_data_csv_load_failure():