fix: handle endif lines in deep copies of variation trees

Author: eugen-shulimov

src/main/java/org/variantsync/diffdetective/variation/tree/VariationNode.java

@@ -483,6 +483,9 @@ public VariationTreeNode<L> toVariationTree(final Map<? super T, VariationTreeNo
             getLineRange(),
             getLabel()
         );
+        if (getEndIf() != null) {
+            newNode.setEndIf(getEndIf());
+        }
         oldToNew.put(this.upCast(), newNode);
 
         for (var child : getChildren()) {