fix mypy

Author: jakeane

flask_pydantic_spec/flask_backend.py

@@ -195,7 +195,8 @@ def validate(
 
         before(request, response, req_validation_error, None)
         if req_validation_error:
-            abort(response)  # type: ignore[unused-ignore]
+            assert response is not None  # response is set when req_validation_error occurs
+            abort(response)
 
         response = make_response(func(*args, **kwargs))