[Lens] Use fireEvent for flyout close-button click to fix Jest timeout (#290263)

Fixes #290124

### Summary
- The only case using `await userEvent.click`
(`flyout_wrapper.test.tsx:92`) hit the 5000 ms timeout under CI parallel
load, while the three synchronous cases rendering the same component
passed — the async interaction machinery, not the assertion, ran out of
budget.
- The close button's handler is a plain synchronous
`onClick={onCancel}`, so nothing needs awaiting. This swaps
`userEvent.click` for `fireEvent.click` (which RTL still wraps in
`act`), removing the pointer/actionability/tooltip-timer overhead while
the `expect(onCancel).toHaveBeenCalledTimes(1)` still reads
synchronously.

| Runtime vs. 5s budget | Passed | Avg | Max |
| --- | --- | --- | --- |
| Before fix | 25/25 | 66ms | 106ms |
| After fix | 25/25 | 24ms | 27ms |

### Context
- Follows the [failed-test investigator's proposed
fix](#290124 (comment))
verbatim; independent code review of `flyout_wrapper.tsx:112`
(`onClick={onCancel}`) and the test file confirmed the diagnosis is
still current.
- Failures were on `kibana-on-merge - main` (Jest Tests), reported twice
— first on 2026-09-09 and again on 2026-09-10 with the same `Exceeded
timeout of 5000 ms` signature.
- The close button is wrapped in an `EuiToolTip` that arms show/hide
timers on hover, which is what tipped `userEvent`'s overhead past the 5s
budget under load; the local runtime table above shows the swap cuts the
per-test cost by ~64% and removes the tail.

<details>
<summary>Verification</summary>

#### Verified locally

- ✅ Passed: `node scripts/eslint
x-pack/platform/plugins/shared/lens/public/app_plugin/shared/edit_on_the_fly/flyout_wrapper.test.tsx`
- ✅ Passed: `node scripts/jest
x-pack/platform/plugins/shared/lens/public/app_plugin/shared/edit_on_the_fly/flyout_wrapper.test.tsx`:
25/25 passed before the fix (avg 66ms, max 106ms), 25/25 after (avg
24ms, max 27ms)

#### Not verified locally

- The 5s timeout does not reproduce locally — it only surfaces under CI
parallel load — so the pass counts above cannot prove the flake is gone.
What they do show is that the fix removes the async `userEvent`
machinery and lowers the test's cost, which is the mechanism behind the
timeout.

</details>

> [!NOTE]
> Share feedback in #kibana-qa. Mention `@copilot` to make quick
changes.

> Generated by [Flaky Test
Fixer](https://github.com/elastic/kibana/actions/runs/34463750481) for
#290124 · claude · opus · 270.2 AIC · ⌖ 64.9 AIC · ⊞ 14.5K ·
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Co-authored-by: Claude Opus 4 (1M context) <noreply@anthropic.com>
Co-authored-by: Marco Vettorello <marco.vettorello@elastic.co>

Author: 3 people

x-pack/platform/plugins/shared/lens/public/app_plugin/shared/edit_on_the_fly/flyout_wrapper.test.tsx

@@ -6,8 +6,7 @@
  */
 
 import React from 'react';
-import { screen } from '@testing-library/react';
-import userEvent from '@testing-library/user-event';
+import { fireEvent, screen } from '@testing-library/react';
 import { renderWithReduxStore } from '../../../mocks';
 import { FlyoutWrapper } from './flyout_wrapper';
 import type { FlyoutWrapperProps } from './types';
@@ -89,7 +88,7 @@ describe('Flyout wrapper', () => {
     it('should call onCancel when the header close button is clicked', async () => {
       const { onCancel } = mountFlyoutWrapper();
 
-      await userEvent.click(screen.getByTestId('euiFlyoutCloseButton'));
+      fireEvent.click(screen.getByTestId('euiFlyoutCloseButton'));
 
       expect(onCancel).toHaveBeenCalledTimes(1);
     });