[5.5] Add new methods to QueueFake and NotificationFake

[mateusjatenee]

Hey guys — sorry for the PR spam, I imagine this is annoying, but I don't feel I should have sent them together.

This PR adds the ability to check if a notification was sent a number of times and to check no notifications were sent:

Notification::assertSentTo($user, Notification::class, 5);

Notification::assertNothingSent();

And it adds the ability to check that no jobs were pushed to the queue.

Queue::assertNothingPushed();

I didn't test NotificationFake methods (PR with automated tests #20650) but I can test them in the morning 👍