[13.x] Add assertPushedOnce()

[weshooper]

PhpStorm flaps about parameters matching default values:

- Queue::assertPushedTimes(JobsComingOutOurEarsJob::class, 1);
+ Queue::assertPushedTimes(JobsComingOutOurEarsJob::class);

But that reads weird. This reads nicer and silences the IDE:

- Queue::assertPushedTimes(JobsComingOutOurEarsJob::class, 1);
+ Queue::assertPushedOnce(JobsComingOutOurEarsJob::class);