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_diffmode.vim b/src/testdir/test_diffmode.vim
index 07aa919..a251d3f 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -801,7 +801,7 @@
   call term_sendkeys(a:buf, ":diffupdate!\<CR>")
   " trailing : for leaving the cursor on the command line
   call term_sendkeys(a:buf, ":set diffopt=internal,filler" . a:extra . "\<CR>:")
-  call term_wait(a:buf)
+  call TermWait(a:buf)
   call VerifyScreenDump(a:buf, a:dumpfile, {})
 endfunc