Add workaround for Intl.NumberFormat mysteriously undefined in unit tests

Author: wojtekmaj

packages/react-datetime-picker/vitest.setup.ts

@@ -1,8 +1,15 @@
-import { afterEach } from 'vitest';
+import { afterEach, beforeEach } from 'vitest';
 import { cleanup } from '@testing-library/react';
 import '@testing-library/jest-dom/vitest';
 import 'vitest-canvas-mock';
 
+// Workaround for a bug in Vitest 3 or happy-dom
+const IntlNumberFormat = Intl.NumberFormat;
+
+beforeEach(() => {
+  Intl.NumberFormat = IntlNumberFormat;
+});
+
 afterEach(() => {
   cleanup();
 });