Safari 16 and 17 runners are no longer reliably available in CI. Saucelabs
still provides them, but session creation failures have been frequent for
weeks now. When this has happened in the past, it's been a prelude to
Saucelabs dropping the affected Safari versions altogether.
We could live with retrying ~30-50% of test runs in the hope that things
might improve, but it's probably better to just rip the band-aid off.
