test(server): reduce parallel number of workers to avoid OOM in CI

apps/server/vite.config.mts

@@ -28,6 +28,7 @@ export default defineConfig(() => ({
       provider: 'v8' as const,
       reporter: [ "text", "html" ]
     },
-    pool: "vmForks"
+    pool: "vmForks",
+    maxWorkers: 8
   },
 }));