TestDoInBackgroundUntilStopped is flaky

[brikis98]

The TestDoInBackgroundUntilStopped test is failing intermittently:

=== RUN   TestDoInBackgroundUntilStopped
=== PAUSE TestDoInBackgroundUntilStopped
=== CONT  TestDoInBackgroundUntilStopped
TestDoInBackgroundUntilStopped 2021-06-21T14:48:51Z retry.go:170: Executing action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:48:51Z retry.go:174: Sleeping for 5s before repeating action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:48:56Z retry.go:170: Executing action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:48:56Z retry.go:174: Sleeping for 5s before repeating action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:49:01Z retry.go:170: Executing action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:49:01Z retry.go:174: Sleeping for 5s before repeating action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:49:06Z retry.go:170: Executing action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:49:06Z retry.go:174: Sleeping for 5s before repeating action 'TestDoInBackgroundUntilStopped'
TestDoInBackgroundUntilStopped 2021-06-21T14:49:06Z retry.go:180: Received stop signal for action 'TestDoInBackgroundUntilStopped'.
=== CONT  TestDoInBackgroundUntilStopped
    retry_test.go:128: 
        	Error Trace:	retry_test.go:128
        	Error:      	Not equal: 
        	            	expected: 3
        	            	actual  : 4
        	Test:       	TestDoInBackgroundUntilStopped
    retry_test.go:131: 
        	Error Trace:	retry_test.go:131
        	Error:      	Not equal: 
        	            	expected: 3
        	            	actual  : 4
        	Test:       	TestDoInBackgroundUntilStopped
--- FAIL: TestDoInBackgroundUntilStopped (30.01s)

The test relies on timing, so it's most likely affected when there is a lot of concurrency on the CI server.