Don't normalize projections referencing type error

[compiler-errors]

Please see UI test for example referenced here: If we try to equate the projection goal <[type error] as Mirror>::Assoc against an impl header that looks like <Wrapper<?0> as Mirror>::Assoc, this will succeed without constraining ?0 since [type error] unifies with everything.

This means that sometimes we can get a non-ambiguous response that does not constrain a projection, which causes these assertions to trigger in some UI tests:

rust/compiler/rustc_hir_typeck/src/writeback.rs

Lines 139 to 142 in eee6b31

	assert!(
	!ty.has_infer() && !ty.has_placeholders() && !ty.has_free_regions(),
	"{ty} can't be put into typeck results"
	);

rust/compiler/rustc_traits/src/normalize_erasing_regions.rs

Line 50 in eee6b31

debug_assert!(!erased.has_infer(), "{erased:?}");

r? @lcnr

[rustbot]

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor