[test] Debug print on test runner timeout

TBR=tmrts@chromium.org
NOTRY=true

Bug: v8:9098
Change-Id: I69d9cd21ad70357a77b45e97393949f1cfbab529
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1557137Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60669}

tools/testrunner/testproc/timeout.py

@@ -25,4 +25,5 @@ class TimeoutProc(base.TestProcObserver):
   def _on_event(self):
     if not self.is_stopped:
       if time.time() - self._start > self._duration_sec:
+        print('>>> Total timeout reached.')
         self.stop()