add missing requirement

Author: willforde

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
       - name: Install test dependencies
         run: |
           python -m pip install --upgrade --no-cache-dir pip
-          pip install --no-cache-dir tox
+          pip install --no-cache-dir tox tox-gh-actions
 
       - name: Test using tox
         run: tox