Hardcode python3.8 for static analysis tests in github actions

Author: farleyb-amazon

.github/workflows/ci_static-analysis.yaml

@@ -34,7 +34,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v1
         with:
-          python-version: 3.x
+          python-version: 3.8
       - run: |
           python -m pip install --upgrade pip
           pip install --upgrade -r ci-requirements.txt