[interop][SwiftToCxx] NFC, add missing include to swift-class-execution.cpp test

Author: hyp

test/Interop/SwiftToCxx/class/swift-class-execution.cpp

@@ -51,6 +51,7 @@
 #include <assert.h>
 #include "class.h"
 #include <cstdio>
+#include <utility>
 
 extern "C" size_t swift_retainCount(void * _Nonnull obj);