patch 9.0.0266: compiler warning for unused argument

Problem:    Compiler warning for unused argument.
Solution:   Add UNUSED.
diff --git a/src/version.c b/src/version.c
index ac14bbd..50294f8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -728,6 +728,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    266,
+/**/
     265,
 /**/
     264,