fix wrong include path in curses-panel module

Unfortunately Python 3.6 doesn't include all autoconfig
infrastructure required for the upstream solution, so we have
to directly patch Modules/_curses_panel.c

Discussion still continue on gh#python#56480.

Author: mcepl

Modules/_curses_panel.c

@@ -14,7 +14,7 @@ static const char PyCursesVersion[] = "2.1";
 
 #include "py_curses.h"
 
-#include <panel.h>
+#include <ncurses/panel.h>
 
 typedef struct {
     PyObject *PyCursesError;