docs(unit-test): stub visualViewport to prevent crashes in JSDOM (#21984)

Resolves #21692

Author: antonhansson0624

packages/vuetify/test/setup/unit-setup.ts

@@ -1,6 +1,11 @@
-import { afterEach } from 'vitest'
+import { afterEach, vi } from 'vitest'
 import { cleanup } from '@testing-library/vue'
 
+// Stub visualViewport so Vuetify components (e.g. VMenu) don't crash in JSDOM
+if (!globalThis.visualViewport) {
+  vi.stubGlobal('visualViewport', new EventTarget())
+}
+
 afterEach(() => {
   cleanup()
 })