games/exult-devel: Update to 20230818 snapshot

ChangeLog:
https://github.com/exult/exult/compare/snapshot-v1.9.0.20230806...snapshot-v1.9.0.20230818

games/exult-devel/Makefile

 DISTVERSIONPREFIX=	snapshot-v
-DISTVERSION=	1.9.0.20230806
+DISTVERSION=	1.9.0.20230818
 PORTREVISION=	0
 PKGNAMESUFFIX=	-devel
 

games/exult-devel/distinfo

-TIMESTAMP = 1691326634
-SHA256 (exult-exult-snapshot-v1.9.0.20230806_GH0.tar.gz) = b8352adc4d463fdaa8f6c9f972c4049a5e49d57ba5bfc44b8470f99c2e83de0a
-SIZE (exult-exult-snapshot-v1.9.0.20230806_GH0.tar.gz) = 19309483
+TIMESTAMP = 1692881596
+SHA256 (exult-exult-snapshot-v1.9.0.20230818_GH0.tar.gz) = b85e11f07d22eab8361a88e55fdf9b06291d46b1af51534a3929010d6dc9e246
+SIZE (exult-exult-snapshot-v1.9.0.20230818_GH0.tar.gz) = 19309903