Rollup merge of #121025 - oli-obk:taint_after_errors, r=petrochenkov

add known-bug tests for derive failure to detect packed repr

We only taint if it was a normal item. Modules and imports are untouched. Tainting them needs to be done differently, and it's unclear if that would be useful or desirable. If we just taint them into `Res::Err`, we end up losing some duplicate name messages *in the presence of other resolution errors*.

r? `@petrochenkov`

Author: matthiaskrgr