patch 8.2.0533: tests using term_wait() can still be flaky

Problem:    Tests using term_wait() can still be flaky.
Solution:   Increase the wait time when rerunning a test. (James McCoy,
            closes #5899)  Halve the initial times to make tests run faster
            when there is no rerun.

src/testdir/test_startup_utf8.vim

@@ -74,7 +74,7 @@ func Test_detect_ambiwidth()
 	\ 'redraw',
 	\ ], 'Xscript')
   let buf = RunVimInTerminal('-S Xscript', {})
-  call term_wait(buf)
+  call TermWait(buf)
   call term_sendkeys(buf, "S\<C-R>=&ambiwidth\<CR>\<Esc>")
   call WaitForAssert({-> assert_match('single', term_getline(buf, 1))})