Fix clippy::println_empty_string, clippy::while_let_on_iterator, clippy::while_let_on_iterator lint style violations (#36613)

Related: #36577

Release Notes:

- N/A

crates/agent2/src/thread.rs

@@ -163,7 +163,7 @@ impl UserMessage {
                     if !content.is_empty() {
                         let _ = write!(&mut markdown, "{}\n\n{}\n", uri.as_link(), content);
                     } else {
-                        let _ = write!(&mut markdown, "{}\n", uri.as_link());
+                        let _ = writeln!(&mut markdown, "{}", uri.as_link());
                     }
                 }
             }