Fix argument name use after applying declaration fix.

Author: aardvark179

src/main/java/org/truffleruby/cext/CExtNodes.java

@@ -128,7 +128,7 @@ protected Object callWithCExtLockAndFrame(
                 Object receiver, RubyArray argsArray, Object specialVariables, Object block,
                 @Cached MarkingServiceNodes.GetMarkerThreadLocalDataNode getDataNode) {
             final ExtensionCallStack extensionStack = getDataNode.execute().getExtensionCallStack();
-            extensionStack.push(variables, block);
+            extensionStack.push(specialVariables, block);
             try {
                 return callCextNode.execute(receiver, argsArray);
             } finally {