test(picker-internal): reduce flakiness of picker internal screenshot test (#28456)

Issue number: N/A

---------

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Sometimes the screenshot gets captured as

![actual](https://github.com/ionic-team/ionic-framework/assets/14926794/dd596788-f871-45b8-ad0b-f8d3682404e4)

when it should be

![expected](https://github.com/ionic-team/ionic-framework/assets/14926794/4807e447-3a02-44e5-95a3-04f1ee742072)

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- Hopefully the screenshot will be more consistent.

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->

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screenshots of how the component looks before and after the change. -->

core/src/components/picker-internal/test/basic/picker-internal.e2e.ts

@@ -9,6 +9,14 @@ configs({ directions: ['ltr'] }).forEach(({ title, screenshot, config }) => {
     test('inline pickers should not have visual regression', async ({ page }) => {
       await page.goto(`/src/components/picker-internal/test/basic`, config);
 
+      const fullStack = page.locator('#inline button[data-value="full-stack"]');
+      const onion = page.locator('#inline button[data-value="onion"]');
+
+      await expect(fullStack).toHaveClass(/picker-item-active/);
+      await expect(onion).toHaveClass(/picker-item-active/);
+
+      await page.waitForChanges();
+
       await expect(page.locator('#inline')).toHaveScreenshot(screenshot(`picker-internal-inline-diff`));
     });
   });