This PR starts running test-go-pg on macOS and Windows in regular CI.
Previously this suite was only run in the nightly gauntlet for 2
reasons:

- it was flaky
- it was slow (took 17 minutes)

We've since stabilized the flakiness by switching to depot runners,
using ram disks, optimizing the number of tests run in parallel, and
automatically re-running failing tests. We've also [brought
down](#17756) the time to run the
suite to 9 minutes. Additionally, this PR allows test-go-pg to use cache
from previous runs, which speeds it up further. The cache is only used
on PRs, `main` will still run tests without it.

This PR also:

- removes the nightly gauntlet since all tests now run in regular CI
- removes the `test-cli` job for the same reason
- removes the `setup-imdisk` action which is now fully replaced by
[coder/setup-ramdisk-action](https://github.com/coder/setup-ramdisk-action)
- makes 2 minor changes which could be separate PRs, but I rolled them
into this because they were helpful when iterating on it:
- replace the `if: always()` condition on the `gen` job with a `if: ${{
!cancelled() }}` to allow the job to be cancelled. Previously the job
would run to completion even if the entire workflow was cancelled. See
[the GitHub
docs](https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/evaluate-expressions-in-workflows-and-actions#always)
for more details.
- disable the recently added `TestReinitializeAgent` since it does not
pass on Windows with Postgres. There's an open issue to fix it:
coder/internal#642

This PR will:

- unblock #15109
- alleviate coder/internal#647

I tested caching by temporarily enabling cache upload on this PR: here's
[a
run](https://github.com/coder/coder/actions/runs/15119046903/job/42496939341?pr=17853#step:13:1296)
showing cache being used.