Auto merge of #102091 - RalfJung:const_err, r=oli-obk

Auto merge of #102091 - RalfJung:const_err, r=oli-obk

make const_err a hard error

This lint has been deny-by-default with future incompat wording since [Rust 1.51](https://github.com/rust-lang/rust/pull/80394) and the stable release of this week starts showing it in cargo's future compat reports. I can't wait to finally get rid of at least some of the mess in our const-err-reporting-code. ;)

r? `@oli-obk`
Fixes https://github.com/rust-lang/rust/issues/71800
Fixes https://github.com/rust-lang/rust/issues/100114