Fix compile of src/tutorial/funcs.c

I broke this with recent #include removals.  Fix by adding an explicit

Reported-by: Devrim Gündüz <devrim@gunduz.org>
Discussion: https://postgr.es/m/5e2c2d7c44434f3f0af7523864b27fe4fb590902.camel@gunduz.org

src/tutorial/funcs.c

@@ -13,6 +13,7 @@
 #include "executor/executor.h"	/* for GetAttributeByName() */
 #include "utils/fmgrprotos.h"	/* for text_starts_with() */
 #include "utils/geo_decls.h"	/* for point type */
+#include "varatt.h"				/* for VARDATA/VARSIZE macros */
 
 PG_MODULE_MAGIC;