chore(deps): update mysql docker tag to v9.6

Author: renovate[bot]

.github/workflows/phpunit.yml

@@ -15,7 +15,7 @@ jobs:
 
     services:
       mysql:
-        image: mysql:9.5
+        image: mysql:9.6
         env:
           MYSQL_ROOT_PASSWORD: root
           MYSQL_DATABASE: wordpress_test