Bring back testing with MySQL

The original reason was after the `rank` becoming a protected keyword. As we depend on doctrine as abrstraction a lot it is good to verify that the translation is reasonable on backend SQL servers of whatever dialect.

Author: Michael Vasseur

.github/workflows/integration.yml

@@ -17,16 +17,23 @@ jobs:
     container:
       image: domjudge/gitlabci:24.04
       options: --privileged --cgroupns=host --init
+    strategy:
+      matrix:
+        include:
+          - sql: mariadb
+            sql_options: --health-cmd="healthcheck.sh --connect --innodb_initialized" --health-interval=10s --health-timeout=5s --health-retries=3
+          - sql: mysql
+            sql_options: ''
     services:
       sqlserver:
-        image: mariadb
+        image: ${{ matrix.sql }}
         ports:
           - 3306:3306
         env:
           MYSQL_ROOT_PASSWORD: root
           MYSQL_USER: domjudge
           MYSQL_PASSWORD: domjudge
-        options: --health-cmd="healthcheck.sh --connect --innodb_initialized" --health-interval=10s --health-timeout=5s --health-retries=3
+        options: ${{ matrix.sql_options }}
     steps:
       - uses: actions/checkout@v4
       - name: info