[buildbot] Fix the buildbot not updating the build status

Summary: The harbormaster api changed since the last buildbot deployment, so update accordingly.

Test Plan: Since it is a simple change I manually edited and restarted the bot container to check it works and there is no other error.

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D13108