Rollup merge of #146439 - connortsui20:fix-sync-macro-attr, r=RalfJung

fix cfg for poison test macro

Fixes test regression in rust-lang/rust#144648
Continuation of rust-lang/rust#146433

I think this is right? Not really sure how to test this myself to be honest.

r? ```@RalfJung```

I'll also leave the improvement to the test macro for a separate PR (described [here](rust-lang/rust#146433 (comment))) since I've never done something like that before. Though since this fixes all of the tests, it might not be necessary since anyone in the future will see the `cfg()` and not `cfg_attr()`?

Author: Zalathar