test: add regression cases for valtree hashing ICE

[Dushyanthyadav]

This PR extends the existing regression test printing_valtrees_supports_non_values.rs to cover cases that previously caused an ICE in const_kind.rs due to hashing inference variables.

It specifically adds:

A case where an associated constant is used without the required trait bound.

The 0: _ case as suggested in Here

Fixes #150409

[rustbot]

r? @davidtwco

rustbot has assigned @davidtwco.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer