Duplicated lifetime name in diagnostic for higher-ranked type in higher-ranked trait bound

[cjgillot]

In https://github.com/rust-lang/rust/pull/101454/files#diff-46c19c4c60dbf4dc95fd23bdb31dbba31d7001a7f269c4068c536522a09f25deR1

The diagnostic looks a bit silly. I don't know why we are choosing a 'b for the inner param.

Originally posted by @cjgillot in #101454 (comment)

[Rageking8]

@rustbot label +T-compiler +A-diagnostics