[element model] fix enclosingElement2 for labels

Chatting with Konstantin, it seems like returning null here (as we do for local functions) is the appropriate response.

Addresses breakage seen in: https://github.com/dart-lang/core/actions/runs/11939711347/job/33280807310#step:6:150


Change-Id: Iaafef66f2c66ceb95ddce34d4a4bd119a9b2b93c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/396702
Commit-Queue: Phil Quitslund <[email protected]>
Auto-Submit: Phil Quitslund <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: pq

pkg/analyzer/lib/src/dart/element/element.dart

@@ -6418,8 +6418,7 @@ class LabelElementImpl2 extends ElementImpl2
   LabelElement2 get baseElement => this;
 
   @override
-  ExecutableElement2? get enclosingElement2 =>
-      super.enclosingElement2 as ExecutableElement2?;
+  ExecutableElement2? get enclosingElement2 => null;
 
   @override
   LabelFragment get firstFragment => _wrappedElement;