Cap ansible-compat in GitHub workflow

ansible-compat 4 includes breaking changes which are incompatible
with older versions of Molecule. Compatibility should be restored
in the Molecule 5.x line but this also contains backwards
incompatible changes which should be reviewed

.github/workflows/molecule.yml

@@ -34,7 +34,8 @@ jobs:
         with:
           python-version: '3.9'
       - name: Install Ansible & Molecule
+        # TODO: review upgrade to Molecule 5.x
         run: pip install "ansible<8" ansible-lint flake8 \
-          "molecule<5" molecule-plugins[docker] pytest-testinfra
+          "molecule<5" "ansible-compat<4" molecule-plugins[docker] pytest-testinfra
       - name: Run Molecule
         run: cd ansible && molecule test -s "${{ matrix.scenario }}"