Actually run tests on PHP 8.1

Author: schmengler

.github/workflows/tests.yml

@@ -120,7 +120,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: M2 Integration Tests with Magento 2
-        uses: extdn/github-actions-m2/magento-integration-tests/7.4@master
+        uses: extdn/github-actions-m2/magento-integration-tests/8.1@master
         with:
           module_name: TddWizard_Fixtures
           composer_name: tddwizard/magento2-fixtures