GCI: Don't try to eval / collect mono items inside overly generic free const items
Fixes#136156. Thanks for the pointers, errs!
There's one (preexisting) thing of note (maybe?). There's a difference between `const _: () = panic!();` and `const _<'a>: () = panic!();`: The former is a pre-mono error, the latter is a post-mono error. For comparison, both `fn _f() { const { panic!() } }` and `fn _f<'a: 'a>() { const { panic!() } }` are post-mono errors.
cc `@oli-obk`
r? compiler-errors or reassign
