Milo doesn't colour steps with a result of WARNING orange for LUCI builds.

For example, compare the "run translation_unit clang tool" steps between these two builds:
LUCI: https://ci.chromium.org/p/infra/builders/luci.infra.codesearch/codesearch-gen-chromium-win/1638
Buildbot: https://uberchromegw.corp.google.com/i/chromium.infra.codesearch/builders/codesearch-gen-chromium-win/builds/564