RandomSamplerTest is flaky on GHA

[clairemcginty]

RandomSamplerTest fails like 5% of builds with errors like:

RandomSamplerTest:
PoissonSampler
  - should work *** FAILED *** (297 milliseconds)
  - 0.06399999999999995 was not less than 0.0544280747619 (RandomSamplerTest.scala:70)

(sample failed run.)