Pin protobuf to 3.20.2 on macOS (#121918)
The newer protobuf 5.26.0 releasing on March 13rd is causing failures with `test_hparams_*` from `test_tensorboard` in which the stringify metadata is wrong when escaping double quote. For example, https://hud.pytorch.org/pytorch/pytorch/commit/3bc2bb678150e02bfa2552b82572d771a892d0c3. This looks like an upstream issue from Tensorboard where it doesn't work with this brand new protobuf version https://github.com/tensorflow/tensorboard/blob/master/tensorboard/pip_package/requirements.txt#L29
The package has been pinned on Docker https://github.com/pytorch/pytorch/blob/main/.ci/docker/requirements-ci.txt#L155, so it should be pinned on macOS too. We want to eventually just have one requirements.txt file.
Fixes https://github.com/pytorch/pytorch/issues/122008
Fixes https://github.com/pytorch/pytorch/issues/121927
Fixes https://github.com/pytorch/pytorch/issues/121946
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121918
Approved by: https://github.com/kit1980
