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)
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index f2a763a..176d282 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -54,6 +54,9 @@
   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 @@
   let g:bwe = []
   let g:brp = []
   set shortmess+=F
+  messages clear
 
   let dirname='XVimTestSHM'
   call mkdir(dirname, 'R')
diff --git a/src/version.c b/src/version.c
index 50773f8..35c1eea 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1456,
+/**/
     1455,
 /**/
     1454,