style: update code to fix pylint failures

The upgrade from pylint 3.1.0 to 3.2.0 resulted in some pylint failures. This commits modifies the code to correct those failures.

edx_name_affirmation/tests/test_api.py

@@ -103,6 +103,7 @@ def test_create_verified_name_empty_string(self, verified_name, profile_name):
         """
         Test that an empty verified_name or profile_name will raise an exception.
         """
+        field = ''
         if verified_name == '':
             field = 'verified_name'
         elif profile_name == '':