Hopefully this finally fixes the double commenting
issue (e.g. odoo/odoo#28160). This seems (according to reading the
logs and also logic) like a failure (concurrency of some sort) leading
to a transaction rollback *after* the GH API call, so the cron's DB
actions are rollbacked (then performed again on the next run) *but*
the GH API interactions are not rollbacked, and are thus performed
twice.
Since the entire purpose of the feedback table is to send comments,
send both "staging failed" and "Linked pull requests" comments via
that.
Before this change, when staging batches only affecting one repo (of n)
the unaffected repositories would get a staging branch exactly matching
the target.
As a result, either runbot_merge or runbot would simply return the
result of an unrelated build, potentially providing incorrect
information and either failing a staging which should have succeeded
(e.g. change in repo A broke B, PR is making a change in repo A which
fixes B, but B's state is reported as the previous broken build) or
succeeding a staging which should have failed (change in repo A breaking
B except a previous build of the exact same B succeeded with a different
A and is returned).
To fix this issue, create a dummy commit at the head of each staging
branch. Because commit dates are included in the hash and have a second
precision it's pretty unlikely that we can get built duplicates, but
just to be completely sure some random bits are added to the commit
message as well.
Various tests fixed to correctly handle the extra dummy commit on
staging branches.
fixes#35
