Fix problem with GCC 11 and Partio's ZIP manager (missing #include <memory>)

Closes #2219 on GitHub. Same fix, but puts the include closer to the copyright header.

Author: Semphris

external/partio_zip/zip_manager.hpp

@@ -1,8 +1,12 @@
 // SOURCE: https://github.com/wdas/partio/blob/main/src/lib/io/ZIP.h
+// NOTE: This file was edited for purposes of compatibility with SuperTux.
 
-/*
+// This include has been added to fix a problem with GCC 11+ (and maybe 10)
+#include <memory>
+
+// =============================================================================
 
-NOTE: This file was edited for purposes of compatibility with SuperTux.
+/*
 
 PARTIO SOFTWARE
 Copyright 2010 Disney Enterprises, Inc. All rights reserved