chore: Fix main CI after upgrade to Rust 1.78 (#11402)

The CI was green at the time I've merged Rust 1.78, but a change that
violated clippy::empty_doc has slipped through into main in the
meantime. Mea culpa, I should've reran the CI.



Release Notes:

- N/A

crates/assistant2/src/attachments.rs

@@ -117,7 +117,6 @@ impl UserAttachmentStore {
     }
 }
 
-///
 pub trait AttachmentTool {
     type Output: 'static;
     type View: Render;