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.
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index dac90aa..0cabd5c 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1062,7 +1062,7 @@
   END
   call writefile(lines, 'XtestBufferScroll')
   let buf = RunVimInTerminal('-S XtestBufferScroll', #{rows: 10})
-  call term_wait(buf, 100)
+  call TermWait(buf, 50)
   call VerifyScreenDump(buf, 'Test_job_buffer_scroll_1', {})
 
   " clean up