patch 8.2.5023: substitute overwrites allocated buffer

Problem:    Substitute overwrites allocated buffer.
Solution:   Disallow undo when in a substitute command.
diff --git a/src/version.c b/src/version.c
index 9751865..cd6c331 100644
--- a/src/version.c
+++ b/src/version.c
@@ -735,6 +735,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    5023,
+/**/
     5022,
 /**/
     5021,