Split CI to run jobs in parallel

[n-batalha]

I shaved some minutes from the CI (In the scenario of caches being hit, the most common?) by splitting various test types into their own jobs, to run them in parallel.
So it's as fast as its slowest job (Windows integration tests), rather than unrelated tests waiting on others.

I guess the DX improves too, to more quickly visualise failing tests on the job list (instead of needing to open a job to look for the failing step).

Before:

After (sometimes 6min, not sure why the large variance):

(Edit: apologies, I created duplicate PRs because it seems I can't force push and reopen #14460)

[n-batalha]

Now that the workflow is finally running, I see that the Windows job is running slower here than in my repo (with the same workflow). You have more actions running in parallel from other branches, whereas I only had my own workflow running, so perhaps there is a runner bottleneck too.
Mine:

https://github.com/n-batalha/tailwindcss/actions/runs/10955846499/job/30422079568?pr=2

Yours:

https://github.com/tailwindlabs/tailwindcss/actions/runs/10956650806/job/30438139771?pr=14476

See Docs for larger runners

[n-batalha]

Discussing separately, the team improved the Windows jobs (the slowest) and might prefer it serially, closing for now