Rollup merge of #149299 - adwinwhite:next-245-ice, r=lcnr

Fudge infer vars in the cause code of `Obligation` intentionally

Fixes the ICE variant in rust-lang/trait-system-refactor-initiative#245.
Fixes rust-lang/rust#142866.

The detailed cause is in the test comments.

r? `@lcnr`

Author: matthiaskrgr