patch 8.2.1498: on slow systems tests can be flaky

Problem:    On slow systems tests can be flaky.
Solution:   Use TermWait() instead of term-wait(). (Yegappan Lakshmanan,
            closes #6756)
diff --git a/src/testdir/test_display.vim b/src/testdir/test_display.vim
index 49d0d8c..bfcb485 100644
--- a/src/testdir/test_display.vim
+++ b/src/testdir/test_display.vim
@@ -250,7 +250,7 @@
 
   let buf = RunVimInTerminal('', #{cols: 20})
   call term_sendkeys(buf, ":call setline(1, repeat('a', 21))\<CR>")
-  call term_wait(buf)
+  call TermWait(buf)
   call term_sendkeys(buf, "O\<Esc>")
   call VerifyScreenDump(buf, 'Test_display_scroll_at_topline', #{rows: 4})