Bug: when automerge fails at the end of a job it causes job to fail

[motatoes]

Scenario: auto_merge is set to true in digger.yml, however the PR has not met all the required status checks. In this case the last job in digger apply has the backend attempting to merge the PR but failing because of response from github API. This causes the apply job to incorrectly fail.

What should happen instead is that the apply job should succeed but the backend should leave an additional comment saying something like: Warning, could not merge the PR automatically, got this error from github: xxxx, please merge it manually