macOS (M1, M2, etc...) compatibility fix for release_21

Changes:

Modified release_21 to make it macOS compatible by upgrading onnx requirement version from 1.12.0 to 1.13.0 and by modifying protobuf version requirements from protobuf>=3.6,<3.20 to protobuf>=3.6,<=3.20.2 both in ./ml-agents and ./ml-agents-envs.