test(core): fix flaky datetime and input-otp tests (#30598)

This fixes the flaky/failing tests here:

`should not have visual regressions with a custom styled calendar`
<img width="1658" height="916" alt="CleanShot 2025-08-04 at 13 46 12@2x"
src="https://github.com/user-attachments/assets/b5d54ee8-b315-4db0-b09b-65d9cd2fa7ca"
/>

`should switch the calendar header when moving to a month with a
different number of days`
<img width="2104" height="1752" alt="CleanShot 2025-08-04 at 13 45
33@2x"
src="https://github.com/user-attachments/assets/8a0cdb0b-6e9d-4b5c-a2df-f9174431492b"
/>

You can run them locally using:

- `npm run test.e2e.docker src/components/datetime/test/datetime.e2e.ts
-- --repeat-each=10`
- `npm run test.e2e.docker
src/components/datetime/test/custom/datetime.e2e.ts -- --repeat-each=10`

---------

Co-authored-by: Brandy Smith <6577830+brandyscarney@users.noreply.github.com>

core/src/components/input-otp/test/separators/input-otp.e2e.ts

@@ -95,6 +95,8 @@ configs({ modes: ['ios'], directions: ['ltr'] }).forEach(({ title, config }) =>
         el.separators = [2, 3];
       });
 
+      await page.waitForChanges();
+
       await expect(await hasSeparatorAfter(page, 0)).toBe(false);
       await expect(await hasSeparatorAfter(page, 1)).toBe(true);
       await expect(await hasSeparatorAfter(page, 2)).toBe(true);