update wording of lint

Author: bryangarza

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -351,7 +351,7 @@ lint_builtin_mutable_transmutes =
 lint_builtin_unstable_features = unstable feature
 
 lint_ungated_async_fn_track_caller = `#[track_caller]` on async functions is a no-op
-     .suggestion = enable this feature
+     .suggestion = enable this unstable feature
 
 lint_builtin_unreachable_pub = unreachable `pub` {$what}
     .suggestion = consider restricting its visibility

compiler/rustc_lint/src/builtin.rs

@@ -1376,7 +1376,7 @@ impl<'tcx> LateLintPass<'tcx> for UngatedAsyncFnTrackCaller {
                     |lint| {
                         lint.span_label(span, "this function will not propagate the caller location");
                         if cx.tcx.sess.is_nightly_build() {
-                            lint.span_suggestion(attr.span, fluent::suggestion, "#[closure_track_caller]", Applicability::MachineApplicable);
+                            lint.span_suggestion(attr.span, fluent::suggestion, "closure_track_caller", Applicability::MachineApplicable);
                         }
                         lint
                     }

src/test/ui/async-await/track-caller/issue-104588-no-op-track-caller.stderr

@@ -2,7 +2,7 @@ warning: `#[track_caller]` on async functions is a no-op
   --> $DIR/issue-104588-no-op-track-caller.rs:4:1
    |
 LL | #[track_caller]
-   | ^^^^^^^^^^^^^^^ help: enable this feature: `#[closure_track_caller]`
+   | ^^^^^^^^^^^^^^^ help: enable this unstable feature: `closure_track_caller`
 LL | async fn foo() {}
    | ----------------- this function will not propagate the caller location
    |

src/test/ui/async-await/track-caller/panic-track-caller.nofeat.stderr

@@ -2,7 +2,7 @@ warning: `#[track_caller]` on async functions is a no-op
   --> $DIR/panic-track-caller.rs:50:1
    |
 LL |   #[track_caller]
-   |   ^^^^^^^^^^^^^^^ help: enable this feature: `#[closure_track_caller]`
+   |   ^^^^^^^^^^^^^^^ help: enable this unstable feature: `closure_track_caller`
 LL | / async fn bar_track_caller() {
 LL | |     panic!()
 LL | | }