patch 9.0.1456: shortmess test depends on order of test execution

Problem:    Shortmess test depends on order of test execution.
Solution:   Clear messages. (closes #12264)

src/testdir/test_autocmd.vim

@@ -54,6 +54,9 @@ if has('timers')
   endfunc
 
   func Test_cursorhold_insert()
+    " depends on timing
+    let g:test_is_flaky = 1
+
     " Need to move the cursor.
     call feedkeys("ggG", "xt")
 
@@ -4215,6 +4218,7 @@ func SetupVimTest_shm()
   let g:bwe = []
   let g:brp = []
   set shortmess+=F
+  messages clear
 
   let dirname='XVimTestSHM'
   call mkdir(dirname, 'R')

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1456,
 /**/
     1455,
 /**/