patch 9.0.0958: messages test is flaky

Problem:    Messages test is flaky.
Solution:   Add a short delay.
diff --git a/src/testdir/test_messages.vim b/src/testdir/test_messages.vim
index ab33caa..ff705fe 100644
--- a/src/testdir/test_messages.vim
+++ b/src/testdir/test_messages.vim
@@ -349,7 +349,7 @@
 
   " display a page and go back, results in exactly the same view
   call term_sendkeys(buf, ' ')
-  call TermWait(buf)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, 'b')
   call VerifyScreenDump(buf, 'Test_verbose_system_1', {})
 
@@ -362,7 +362,7 @@
   call VerifyScreenDump(buf, 'Test_verbose_system_2', {})
 
   call term_sendkeys(buf, ' ')
-  call TermWait(buf)
+  call TermWait(buf, 50)
   call term_sendkeys(buf, 'b')
   call VerifyScreenDump(buf, 'Test_verbose_system_2', {})