Fixing macOS CI and re-enable the truffleruby test on macOS

[eregon]

It was disabled in #5119
and means this bug was not caught: #5385

[eregon]

The failure in macOS CI is unrelated: https://github.com/rvm/rvm/actions/runs/6084945174/job/16507919460?pr=5387
That will need to be fixed first.

[eregon]

So test/fast/* passes now: https://github.com/rvm/rvm/actions/runs/8349160490/job/22852712175?pr=5387
But for some reason truffleruby_comment_test fails without any output.
I wonder if maybe the previous CI steps delete ~/.rvm/scripts/rvm or cause that script to exit with 1.
Or maybe they just change the default ruby being used and tf is not found.

And indeed truffleruby_comment_test passes if run first: https://github.com/eregon/rvm/actions/runs/8349445042/job/22853649326

[eregon]

https://github.com/eregon/rvm/actions/runs/8358105456/job/22878671570
So ~/.rvm/scripts/rvm exists but:

Run source ~/.rvm/scripts/rvm && true
Error: Process completed with exit code 1.

So it seems somehow the fast tests break rvm somehow, to the point it even fails to be sourced and the only error is the exit code, only on macOS (not on Linux).
I'll workaround by running the truffleruby tests first then, that should work fine.