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_termcodes.vim b/src/testdir/test_termcodes.vim
index 524be31..f3a7af5 100644
--- a/src/testdir/test_termcodes.vim
+++ b/src/testdir/test_termcodes.vim
@@ -1898,9 +1898,9 @@
   CheckRunVimInTerminal
   let buf = RunVimInTerminal('', #{rows: 14})
   call term_sendkeys(buf, ":set cmdheight=3\<CR>")
-  call term_wait(buf, 100)
+  call TermWait(buf, 100)
   call term_sendkeys(buf, ":set term=xxx\<CR>")
-  call term_wait(buf, 100)
+  call TermWait(buf, 100)
   call assert_match('builtin_dumb', term_getline(buf, 11))
   call assert_match('Not found in termcap', term_getline(buf, 12))
   call StopVimInTerminal(buf)