Rework spec checking for active job leaks to handle new ActiveJob::TestHelper implementation

[JonRowe]

Rails 8.2 changed the active job test helper in such a way that in certain load orders, the adapter for ActiveJob::Base is cached, this implementation then overrides the configuration which results in our setup during a regression test for checking that queues don't leak between jobs breaking because the job and test have different queues, and the test never sees the job at all let alone leak.

You can verify this locally by using a seed such as 40770, or running the spec in isolation and changing the assertion for the adapter to:

expect {
  ActiveJob::TestHelper::TestQueueAdapter.reset
}.to change { ActiveJob::Base.queue_adapter }.to(test_adapter)