test(browser): pin Date with setSystemTime so it holds under vitest 5.1

tests/browser/clock.ts

@@ -6,9 +6,14 @@
  * is faked: timers, animation frames and the microtask queue keep running,
  * which is what Radix, TanStack Query and the URL-state queue wait on.
  * `setup.ts` restores the real clock after every test.
+ *
+ * `setSystemTime` without fake timers holds `Date` at the given instant.
+ * `useFakeTimers({ toFake: ["Date"] })` did the same until vitest 5.1, where
+ * the faked `Date` moves on with the wall clock and a form submitted a few
+ * hundred milliseconds in no longer sends the pinned instant.
  */
 import { vi } from "vitest";
 
 export function pinDate(iso: string): void {
-  vi.useFakeTimers({ toFake: ["Date"], now: new Date(iso) });
+  vi.setSystemTime(new Date(iso));
 }