[11.x] Adds PHPUnit 11 support

[nunomaduro]

This pull request introduces support for PHPUnit 11 and Pest 3 in Laravel 11. While at the same time, supporting PHPUnit 10 and Pest 2. @taylorotwell, please be aware that we have implemented a few changes at the HandleExceptions level that require your review:

1. We have deprecated the forgetApp method in favor of flushState.
2. The flushState method not only forgets the app instance but also clears every exception|error handler previously set in PHP's global state. If PHPUnit had an error handler, we have reset it to the original one.
3. The decision of clearing every exception|error handler previously set in PHP's global state is an important one. Because:

• It fixes PHPUnit's message regarding Test code or tested code did not remove its own exception handlers.
• It avoids memory leaks any vendor code setting their own exception|error handler hundreds of times on the test suite, because the application boots for every single test case.

@crynobone, could you please review and merge this pull request before we proceed with merging this one?