This PR:
- Reduces test parallelism on Windows in CI
- Unifies wait intervals on Windows with Linux and macOS. Previously we
had custom intervals for Windows to reduce test flakiness on smaller CI
workers, but we don't run tests on small CI workers anymore. Due to how
our CI file is defined, forks run tests on small CI machines, but I'm
not sure if the different intervals actually help or whether that's a
heuristic that happened to fix issues on a particular day and was it
ever reevaluated. I propose we make the change and if someone complains,
revert it.
In particular, reduced test parallelism seems to actually help: I was
able to run Windows tests 5 times in a row without flakes. Not sure if
that's going to fix the problem long term, but it seems worth trying.
