don't alter can_reset_password flag for users without an FC account (#25655)

src/authentic2_auth_fc/__init__.py

@@ -67,7 +67,9 @@ class AppConfig(django.apps.AppConfig):
             serializer.fields['franceconnect'] = serializers.SerializerMethodField()
 
     def a2_hook_user_can_reset_password(self, user):
-        return user.fc_accounts.exists()
+        if user.fc_accounts.exists():
+            return True
+        return None
 
 
 default_app_config = '%s.%s' % (__name__, 'AppConfig')