- Extract update tests into separate tests.
- Make `brew tests --online` run only once in its own job. This job
could be made non-required to fight flakiness.
- Split up the various macOS runs into several steps now that we have
more parallel macOS workers available.
- Cleanup some flaky tests.
Remove pending tests that are never run on CI (i.e. require `--online`),
remove fixtures for those tests and just make `--official-cmd-taps`
run by `--online` instead.