Add voip_unittests to buildbot/manage.py

WebRTC is adding a new test binary to run audio only tests.

Bug: webrtc:11251
Change-Id: I837a2868755f7d3cfeeb16542f6ed55096207a30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134295Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756205}

testing/buildbot/manage.py

@@ -171,6 +171,7 @@ SKIP_GN_ISOLATE_MAP_TARGETS = {
   'tools_unittests',
   'video_engine_tests',
   'voice_engine_unittests',
+  'voip_unittests',
   'webrtc_nonparallel_tests',
   'xmllite_xmpp_unittests',