Fix minor issues found while publishing crates for Arti 0.4.0

These came up when I was running cargo publish today; they are pretty harmless, but still worth fixing.

requested review from @Diziet

assigned to @nickm

I would have done #[allow(unused_imports)] (since this approach seems a bit brittle) but this is fine too.

enabled an automatic merge when the pipeline for 5b1622c2 succeeds

CI failure looks spurious. I think I have got it to retry properly...

final link failed: No space left on device

maybe there is someone to notify?

Perhaps. The problem seems to have been transient. Another job failed in the same way. I choose to assume it has fixed itself via cron or something. We can report it if it keeps happening...

merged

mentioned in commit 58249924