Fix the test-stlite-server CI workflow as a workaround

.github/workflows/main.yml

@@ -144,6 +144,7 @@ jobs:
     - name: Set up Streamlit and build proto
       run: |
         . .venv/bin/activate
+        pip install mypy-protobuf
         make streamlit-proto
 
     - name: Run linter and code formatter to the test code module