NEWS: corrected the definition of convexity of functions

--- a/NEWS	Wed Feb 07 11:52:34 2024 +0000
+++ b/NEWS	Wed Feb 07 11:57:22 2024 +0000
@@ -25,6 +25,9 @@
   by Sledgehammer and should be used instead. For more information, see
   Sledgehammer's documentation relating to "preplay_timeout". INCOMPATIBILITY.
 
+* HOL-Analysis: corrected the definition of convex function (convex_on)
+  to require the underlying set to be convex. INCOMPATIBILITY.
+
 * Explicit type class for discrete_linear_ordered_semidom for integral
   semidomains with a discrete linear order.