vim-patch:9.2.0425: Cannot silence undo/redo messages (#39554)

Problem:  Cannot silence undo/redo messages
Solution: Add "u" flag to 'shortmess' option
          (Shougo Matsushita).

fixes:  vim/vim#20049
closes: vim/vim#20107

d25f8d1b2c

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

runtime/lua/vim/_meta/options.gen.lua

@@ -6099,6 +6099,9 @@ vim.bo.sw = vim.bo.shiftwidth
 --- 	search count statistics.  The maximum limit can be set with
 --- 	the 'maxsearchcount' option, see also `searchcount()`
 --- 	function.
+---   u	don't give undo and redo messages like			*shm-u*
+--- 	"1 line less; before #1  1 second ago", "Already at oldest
+--- 	change" or "Already at newest change"
 ---
 --- This gives you the opportunity to avoid that a change between buffers
 --- requires you to hit <Enter>, but still gives as useful a message as