Investigate slow `test_status_actor` test case on macOS

[ryan-williams]

812031d: skip a macOS-failing test

I thought the same thing at first, but test_status_actor actually does clear for me on Mac after ~10 mins or so. It looks like it's typically one of the slowest tests in CI too. It only takes only ~30 seconds on Ubuntu though (e.g. from this run):

============================== slowest durations ===============================

115.00s call     tests/deduplication/test_decontamination.py::test_exact_decontamination_paragraph

30.53s call     tests/test_executor.py::test_status_actor

14.02s call     tests/test_dry_run.py::test_run_dry_runs[exp474_config_sweep.py]

13.44s call     tests/test_download_pretokenized.py::test_download_and_load_cache

Is there a better way to handle this, maybe with a slow mark that is conditional on macOS?

Originally posted by @eric-czech in #3

@dlwh also added:

my guess is we may need to emulate more CPUs. I'll try to see what Ray thinks it's doing