Update unittests.yaml

Update python 3.9.5

Author: tspreitzer

.github/workflows/unittests.yaml

@@ -8,7 +8,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.12.0
+          python-version: 3.9.5
           architecture: x64
       - name: Install dependencies
         run: pip install -r requirements.txt