Misleading comments over methods on `TyCtxtEnsure` in `rustc_middle::mir::interpret::queries`

[cjgillot]

These comments (also the one below) are wrong now -- they talk about the return value of a function that doesn't return anything! I have no idea what is going on here so if someone could make a PR to update the comments, that would be much appreciated. :)

_Originally posted by @RalfJung in #98238 (comment)