Adjusting LazyWarnNode according to docs

Author: horakivo

src/main/java/org/truffleruby/language/LazyWarnNode.java

@@ -19,12 +19,12 @@
 @GenerateCached(false)
 public abstract class LazyWarnNode extends RubyBaseNode {
 
-    public abstract WarnNode execute(Node node);
-
     public final WarnNode get(Node node) {
         return execute(node);
     }
 
+    protected abstract WarnNode execute(Node node);
+
     @Specialization
     protected static WarnNode doLazy(
             @Cached(inline = false) WarnNode warnNode) {