Set ssl-verify-server-cert to on

Author: swissspidy

.github/workflows/reusable-testing.yml

@@ -393,7 +393,7 @@ jobs:
             # warnings because WP-CLI passes password via the `MYSQL_PWD` environment variable
             # and the setting is otherwise implicitly used.
             [client-mariadb]
-            ssl-verify-server-cert
+            ssl-verify-server-cert = on
 
       - name: Configure DB environment
         if: ${{ matrix.dbtype != 'sqlite' }}