Pin CI `protobuf==3.20.1` (#8015)

Pin protobuf==3.20.1

Resolve protobuf 4 issues.

.github/workflows/ci-testing.yml

       - name: Install requirements
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements.txt coremltools openvino-dev tensorflow-cpu --extra-index-url https://download.pytorch.org/whl/cpu
+          pip install -r requirements.txt protobuf==3.20.1 coremltools openvino-dev tensorflow-cpu --extra-index-url https://download.pytorch.org/whl/cpu
           python --version
           pip --version
           pip list
       - name: Install requirements
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements.txt --extra-index-url https://download.pytorch.org/whl/cpu
+          pip install -r requirements.txt protobuf==3.20.1 --extra-index-url https://download.pytorch.org/whl/cpu
           python --version
           pip --version
           pip list