Fix linting: remove unused json import

Author: kevinfiddlerai

tests/test_fiddler_rails.py

@@ -12,7 +12,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import json
 import os
 from unittest.mock import AsyncMock, MagicMock, patch