patch 9.0.0539: long message test can be flaky

Problem:    Long message test can be flaky.
Solution:   Wait for more prompt instead of ruler.
diff --git a/src/testdir/test_messages.vim b/src/testdir/test_messages.vim
index 140f1c3..a92a580 100644
--- a/src/testdir/test_messages.vim
+++ b/src/testdir/test_messages.vim
@@ -366,7 +366,8 @@
     echom range(9999)->join("\x01")
   END
   call writefile(content, 'Xtest_quit_message')
-  let buf = RunVimInTerminal('-S Xtest_quit_message', #{rows: 6})
+  let buf = RunVimInTerminal('-S Xtest_quit_message', #{rows: 6, wait_for_ruler: 0})
+  call WaitForAssert({-> assert_match('^-- More --', term_getline(buf, 6))})
   call term_sendkeys(buf, "q")
   call VerifyScreenDump(buf, 'Test_quit_long_message', {})
 
diff --git a/src/version.c b/src/version.c
index 0bbeae6..359c70c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    539,
+/**/
     538,
 /**/
     537,