Fix tox version in CI (#374)

Author: carolabadeer

.github/workflows/UnitTesting.yaml

@@ -36,7 +36,7 @@ jobs:
           python-version: ${{ env[matrix.python-version] }}
 
       - name: Install tox
-        run: pip install -U tox-factor
+        run: pip install "tox<=3.27.1" -U tox-factor
 
       - name: Cache tox environment
         # Preserves .tox directory between runs for faster installs