Don't synthesize host effect args inside trait object types

[fmease]

While we were indeed emitting an error for ~const & const trait bounds in trait object types, we were still synthesizing host effect args for them.

Since we don't record the original trait bound modifiers for dyn-Trait in hir::TyKind::TraitObject (unlike we do for let's say impl-Trait, hir::TyKind::OpaqueTy), AstConv just assumes ty::BoundConstness::NotConst in conv_object_ty_poly_trait_ref which given <host> dyn ~const NonConstTrait resulted in us not realizing that ~const was used on a non-const trait which lead to a failed assertion in the end.

Instead of updating hir::TyKind::TraitObject to track this kind of information, just strip the user-provided constness (similar to #119505).

Fixes #119524.

[rustbot]

r? @wesleywiser

(rustbot has picked a reviewer for you, use r? to override)

[compiler-errors]

@bors r+

[bors]

📌 Commit 695a02e has been approved by compiler-errors

It is now in the queue for this repository.

[compiler-errors]

@bors rollup