Check if some `//@ ignore-test` auxiliaries can instead use the canonical `auxiliary/` infra

[jieyouxu]

Some tests are //@ ignore-test because they are auxiliaries / support files, but they aren't placed under canonical auxiliary/ directories. Audit these files to see if they can instead use auxiliary/ infra without regressing test intention.

[jieyouxu]

Update: see #139783

I did another survey pass over //@ ignore-test under tests/, and this is the only 2 non-tests that should use compiletest-ignore-dir.

Other aux test support files have various reasons that they either can't use auxiliary/ directory (majority of cases) or moving aux file under auxiliary/ requires significant changes to the original test (incl. error annotations) that does not justify the churn.

See #t-compiler > Handling disabled `//@ ignore-test` tests @ 💬 for some more discussions.