test(server): try to use threads instead of forks to avoid ELIFECYCLE issues in the CI

apps/server/vite.config.mts

@@ -15,6 +15,7 @@ export default defineConfig(() => ({
       reportsDirectory: './test-output/vitest/coverage',
       provider: 'v8' as const,
       reporter: [ "text", "html" ]
-    }
+    },
+    pool: "threads"
   },
 }));