Pin ansible to 2.16.*

We do the same in the utility container and it keeps the testing a bit
more consistent.

.github/workflows/ansible-unittest.yml

@@ -44,7 +44,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install pytest ansible
+          pip install pytest ansible=='2.16.*'
 
       - name: Run make ansible-sanitytest
         run: |