feat: Add forgotten GR_PLR_DROP_GUN_BEST constant (#374)

Author: Nord1cWarr1or

reapi/extra/amxmodx/scripting/include/cssdk_const.inc

@@ -865,7 +865,9 @@ enum
 	GR_PLR_DROP_GUN_NO,
 	GR_PLR_DROP_AMMO_ALL,
 	GR_PLR_DROP_AMMO_ACTIVE,
-	GR_PLR_DROP_AMMO_NO
+	GR_PLR_DROP_AMMO_NO,
+
+	GR_PLR_DROP_GUN_BEST
 };
 
 /**