Remove deprecated method.

[TingluoHuang]

lint: testing/random.go#L9SA1019: rand.Seed has been deprecated since Go 1.20 and an alternative has been available since Go 1.0: Programs that call Seed and then expect a specific sequence of results from the global random source (using functions such as Int) can be broken when a dependency changes how much it consumes from the global random source. To avoid such breakages, programs that need a specific result sequence should use NewRand(NewSource(seed)) to obtain a random generator that other packages cannot access.  (staticcheck)

https://github.com/actions/actions-runner-controller/actions/runs/4611217178

[nikola-jokic]

I have been meaning to do that for a while now 😄 Thank you for taking care of it!