Fix flaky concurrency controls test

Replace fixed sleeps with deterministic waits in the
"don't block claimed executions that get released" test.

The test was using sleep(0.2) to wait for claiming and
sleep(shutdown_timeout + 0.6) to wait for shutdown, both of
which are timing sensitive and unreliable on slow CI. Instead,
use wait_for to wait for the job to be claimed, and
terminate_process to wait for the supervisor to actually exit.

Author: diogovernier

test/integration/concurrency_controls_test.rb

@@ -166,12 +166,11 @@ class ConcurrencyControlsTest < ActiveSupport::TestCase
     NonOverlappingUpdateResultJob.perform_later(@result, name: "I'll be released to ready", pause: SolidQueue.shutdown_timeout + 10.seconds)
     job = SolidQueue::Job.last
 
-    sleep(0.2)
-    assert job.claimed?
+    wait_for(timeout: 2.seconds) { job.reload.claimed? }
 
-    # This won't leave time to the job to finish
-    signal_process(@pid, :TERM, wait: 0.1.second)
-    sleep(SolidQueue.shutdown_timeout + 0.6.seconds)
+    # Terminate the supervisor and wait for it to fully exit, so workers
+    # have time to deregister and release their claimed executions.
+    terminate_process(@pid)
 
     assert_not job.reload.finished?
     assert job.reload.ready?