ci: fix MySQL connection using TCP instead of Unix socket

MySQL client libraries resolve 'localhost' to a Unix socket path
   (/run/mysqld/mysqld.sock), which does not exist in the containerized
   service. Use 127.0.0.1 to force a TCP connection.

.github/workflows/integration-test.yml

@@ -123,7 +123,7 @@ jobs:
           --health-retries 15
 
     env:
-      DATABASE_URL: "mysql://vaultwarden:vaultwarden@localhost:3306/vaultwarden"
+      DATABASE_URL: "mysql://vaultwarden:vaultwarden@127.0.0.1:3306/vaultwarden"
 
     steps:
       - name: Install dependencies