Rollup merge of #143056 - fmease:mv-ace-test-out-of-gci-dir, r=BoxyUwU

Move an ACE test out of the GCI directory

In rust-lang/rust#122988, a test pertaining to `associated_const_equality` was placed into the directory meant for `generic_const_items`. Let's move it where it belongs.

While at it, I took the time to further minimize the test and to add a description. You can use 1.67.1 (as reported in rust-lang/rust#108220) to verify that I didn't butcher it. For additional context, the issue was likely fixed in rust-lang/rust#112718 (but I'm also cc'ing rust-lang/rust#140467 which further fixed things up and has more context).

I only performed quick and dirty git/GitHub archeology, so I don't have the full picture here. For one, I'm not even sure if this regression test is worth it.

Anyway, I just want it gone from the GCI dir :)

Author: compiler-errors