Fixes:coder/internal#950

Pretty sure the intention of thehold wait group is to try to get the two goroutines that the test starts running at the same time. But, that should be the case for two goroutines started anyway.

The use ofhold doesn't actually guarantee concurrent execution ofAcquire, just that both goroutines get as far asDone() --- the go scheduler could run them serially without incident.

So I've chosen to just remove the use ofhold to simplify.

But, for posterity, the data race was due to incrementing by 1 in the loop along with the goroutine that calls Done. You could increment by 1 and then back down to 0 before the second iteration of the loop starts. This then causes a data race with callingWait() in the first goroutine andAdd() in the second iteration. c.f.https://pkg.go.dev/sync#WaitGroup.Add