[IMP] runbot_merge: make feedback more deterministic

Before this change, the order of PRs to list in an "unready" feedback
message was whatever the DB returned which could vary. This change
fixes the order by applying model order.

runbot_merge/models/pull_requests.py

@@ -763,7 +763,7 @@ class PullRequests(models.Model):
         for [ids] in self.env.cr.fetchall():
             prs = self.browse(ids)
             ready = prs.filtered(lambda p: p.state == 'ready')
-            unready = prs - ready
+            unready = (prs - ready).sorted()
 
             for r in ready:
                 self.env['runbot_merge.pull_requests.feedback'].create({