[ONNX] Add `caffe2/python/onnx/**` to merge rule (#85118)
This PR extends merge rule such that any related fixes needed for caffe2 onnx tests can be merged in the same PR. Test skips need to be added to `caffe2/python/onnx/tests/onnx_backend_test.py` for new ONNX operators when ONNX submodule is updated.
Unblocks #83201
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85118
Approved by: https://github.com/malfet
