rustdoc: Notable traits shows traits for `&[u8]` even though the return type is `&[Attribute]`

[camelid]

This is in the rustc docs, but this can probably be reproduced pretty easily elsewhere.

beta (also on nightly)

stable

Note that there is no notable traits dialog:

[apiraino]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.

@rustbot label -I-prioritize +P-medium

[pietroalbini]

This affected 1.51.0, the regressed behavior is also present on stable. Changing the labels.