Skip failing tests on windows for python3 in on_error_test.py.
Skip failing tests on windows for python3 in on_error_test.py.

Currently Windows tryjob runs Python2 and python3 tests, but ignores results of python3 tests.
Skip failing tests in order to enable Python3 tests on Windows tryjob.

Bug: 1017545, 1182016
Change-Id: If3cf4177cd6cdf12b471c402d72b164e835d57cb
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2730227
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Momo Sasaki <e99fedc53ffce896a4ecf43ecee40bbdb01d5909@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py