Action Cable integration test should soft fail on exit 3

[zzak]

This is to support rails/rails#51990.

Inside the actioncable test:integration job, we capture the output and look for The environment you requested was unavailable which happens far too often: https://buildkite.com/rails/rails/builds/111313#0191e945-faef-4d92-8f8a-74dbd1d397db

If we capture that output, the job will exit 3.

In this PR, we've added a retry policy for 1 extra retry (2 total attempts) and to mark the job as soft_fail if the exit status 3 persists.

This should cut down on flaky builds due to actioncable:integration step failing.

I've tested the behavior locally in various scenarios.