pin protobuf version to 3.20.2

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/456

`3.20.1` version has security issue, as https://github.com/facebookresearch/d2go/security/dependabot/1.`3.20.x+` has previously known compatibility issue, thus pin the version to `3.20.2`.

Reviewed By: YanjunChen329

Differential Revision: D42353218

fbshipit-source-id: 172d3a2d53f0c46326e0ae730ad0a96b33b8bade

setup.py

@@ -33,7 +33,7 @@ requirements = [
     # Downgrade the protobuf package to 3.20.x or lower, related:
     # https://developers.google.com/protocol-buffers/docs/news/2022-05-06#python-updates
     # https://github.com/protocolbuffers/protobuf/issues/10051
-    "protobuf<=3.20.1",
+    "protobuf==3.20.2",
 ]