patch 8.2.4211: window title test still fails in some configurations

Problem:    Window title test still fails in some configurations.
Solution:   Use WaitForAssert().
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 39110bb..edd03e3 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1643,7 +1643,7 @@
   END
   call writefile(lines, 'Xsetbufvar')
   let buf = RunVimInTerminal('-S Xsetbufvar', {})
-  call assert_match('Xa.txt', term_gettitle(buf))
+  call WaitForAssert({-> assert_match('Xa.txt', term_gettitle(buf))}, 1000)
 
   call term_sendkeys(buf, "i\<F2>")
   call TermWait(buf)