Pin protobuf to 3.20.2 on macOS (#121918) (#122207)

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 #122008
Fixes #121927
Fixes #121946
Pull Request resolved: #121918
Approved by: https://github.com/kit1980

(cherry picked from commit 5f601a4)

Co-authored-by: Huy Do <huydhn@gmail.com>

.github/requirements/pip-requirements-macOS.txt

@@ -28,3 +28,6 @@ rockset==1.0.3
 z3-solver==4.12.2.0
 tensorboard==2.13.0
 optree==0.9.1
+# NB: test_hparams_* from test_tensorboard is failing with protobuf 5.26.0 in
+# which the stringify metadata is wrong when escaping double quote
+protobuf==3.20.2