Use #![register_tool] instead of #![register_attr]

CC https://github.com/rust-lang/rust/issues/66079

components/script/script_thread.rs

@@ -434,7 +434,7 @@ impl OpaqueSender<CommonScriptMsg> for Sender<MainThreadScriptMsg> {
 
 /// The set of all documents managed by this script thread.
 #[derive(JSTraceable)]
-#[must_root]
+#[unrooted_must_root_lint::must_root]
 pub struct Documents {
     map: HashMap<PipelineId, Dom<Document>>,
 }