[Docs]: Update example to trigger select-all from keyboard

[scottopherson]

Page(s)

https://playwright.dev/docs/next/api/class-keyboard

Description

playwright/docs/src/api/class-keyboard.md

Lines 106 to 111 in 9eb4fe5

	```js
	// on Windows and Linux
	await page.keyboard.press('Control+A');
	// on macOS
	await page.keyboard.press('Meta+A');
	```

I got stuck on a test that needed to use Control+Enter keypress but was failing in CI. Finding the best OS-agnostic way to do this was tricky until I found #12168 -> #30572 which already had the solution I needed: ControlOrMeta+Enter.

Perhaps:

  // on Windows and Linux
  await page.keyboard.press('Control+A');
  // on macOS
  await page.keyboard.press('Meta+A');
+ // OS-agnostic
+ await page.keyboard.press('ControlOrMeta+A');