chore: add regression test for #22567

[hamzaremmal]

Closes #22567

Most likely closing #22571 too

The last run of Open CB confirmed that it closes #22571 too.

[som-snytt]

The pos test doesn't have -Werror; I think vulpix does not check for "no output" if check file is missing? (Too late in the day for me to verify that.)

I commented on the ticket that my PR that just got merged is the fix (makes the message go away). That PR has something to with how implicit args are conjured in an application.

That test was tests/neg/i22439.scala, I haven't compared yet. Edit: that test doesn't include defaults (for some reason).

There is a default in tests/neg/i19594.scala

[som-snytt]

@hamzaremmal I noticed that my other PR was for your other ticket about implicit args in January, so thanks for that. I don't remember exactly why it caught my attention (probably I thought it would be an easy fix), but I remember it was interesting and I wouldn't have tried it without your ticket.