fix test 'mixed-intro-example-three-loops.cpp2' for gcc 12

Gcc 12 requires to specify header <memory> for using make_unique

Author: knst

regression-tests/mixed-intro-example-three-loops.cpp2

@@ -3,6 +3,7 @@
 #include <vector>
 #include <string>
 #include <span>
+#include <memory>
 
 auto print(auto const& thing) -> void { 
     std::cout << ">> " << thing << "\n";