Put subsuites with a few tests in one group (#47423)
- Put subsuites with a few tests in one group
As we will need to restart the browser when starting a new subsuite,
putting tests in one group can help reduce the number of restarts
needed.
Keep an up limit of the size of such a group, so that we do not create a
huge group that could potentially cause a worker to out live all other
workers, thus increase the run time.