Rollup merge of #140467 - BoxyUwU:no_fcw_assoc_consts, r=lcnr

Don't FCW assoc consts in patterns

Fixes #140447

See comment in added test. We could also check that the anon const is a const arg by looking at the HIR. I'm not sure that's necessary though 🤔 The only consts that are evaluated "for the type system" are const args (which *should* get FCWs) and const patterns (which cant be anon consts afaik).

Author: matthiaskrgr