[8.x] Add Event::fakeExcept() to fake all but certain events

[devfrey]

I sometimes find myself working on feature tests that trigger multiple events. I try to fake all events to avoid unexpected side effects, but sometimes certain events may be required to simulate expected behaviour. I would use this to fake all but certain events:

Event::fake([
    fn (string $eventClass) => $eventClass !== ServiceSaving::class,
]);

This PR adds a new fakeExcept() method to the Event facade to allow this:

Event::fakeExcept(ServiceSaving::class);
Event::fakeExcept([ServiceSaving::class, 'some-other-event']);

[taylorotwell]

Thanks for contributing to Laravel! ❤️