Protobuf update breaks firestore library.

[StormyDragon]

With the release of protocol buffers v21.0 (pypi: protobuf==4.21.0)
Poetry update included it and promptly broke google-cloud-firestore==2.5.0.

File "/app/.venv/lib/python3.10/site-packages/google/cloud/firestore_v1/base_batch.py", line 141, in update
    write_pbs = _helpers.pbs_for_update(
File "/app/.venv/lib/python3.10/site-packages/google/cloud/firestore_v1/_helpers.py", line 941, in pbs_for_update
    update_pb.update_transforms.extend(field_transform_pbs)

TypeError: Expected a message object, but got field_path: "hits"
increment {
  integer_value: 1
}

I'm pinning the older protobuf release until this is fixed.