std.traits: Adapt unittest to pass with -preview=in

[Geod24]

Redo of #7609 after it was reverted because a library relied on a bug that has since been fixed (revert: #7611 , bugfix: #7612 ).

[dlang-bot]

Thanks for your pull request, @Geod24!

Bugzilla references

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7614"

[wilzbach]

Let's wait for Buildkite this time :)

[Geod24]

The commit that broke Buildkite was in #7612 . But yeah, no problem. Also, we should really fix the bug, especially since we're moving stuff away from the auto-tester... And/or make some more checks required ?

[wilzbach]

Also, we should really fix the bug, especially since we're moving stuff away from the auto-tester...

It wasn't a bug here. It was merged manually. The bug only applies to GitHub actions as they aren't returned by the traditional CI APi.

And/or make some more checks required ?

Yes, that's the one. Yesterday I set more checks as required on DMD and I think we just need to do the same here. Considering our history IMHO all CIs should be set as required.

[Geod24]

It wasn't a bug here. It was merged manually. The bug only applies to GitHub actions as they aren't returned by the traditional CI APi.

Also Azure (dlang/dlang-bot#250).