enclosingElement -> enclosingElement3 (#163681)

https://github.com/flutter/flutter/pull/163567#issuecomment-2669969018

The old name is deprecated and removed.

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dev/bots/custom_rules/render_box_intrinsics.dart

@@ -115,7 +115,7 @@ class _RenderBoxSubclassVisitor extends RecursiveAstVisitor<void> {
     if (isCallingSuperImplementation) {
       return;
     }
-    final Element? declaredInClassElement = node.staticElement?.declaration?.enclosingElement;
+    final Element? declaredInClassElement = node.staticElement?.declaration?.enclosingElement3;
     if (declaredInClassElement is InterfaceElement &&
         _implementsRenderBox(declaredInClassElement)) {
       violationNodes.add((node, correctMethodName));