Add missing Redis service to CI workflow.

Author: mgruner

.github/workflows/ci.yml

@@ -11,6 +11,9 @@ jobs:
         env:
           POSTGRES_USER: zammad
           POSTGRES_PASSWORD: zammad
+      redis:
+        # Use Redis 5 which is shipped in Debian 10.
+        image: redis:5
     env:
       ZAMMAD_PHP_API_CLIENT_UNIT_TESTS_URL: "http://localhost:3000"
       ZAMMAD_PHP_API_CLIENT_UNIT_TESTS_USERNAME: "admin@example.com"