The current backport action cannot automerge because
the github action bot does not trigger github CI actions.
Mergify instead does not have this limitation and can also
use a merge queue.
On top we have now a declarative configuration to allow
contributers to add new tests to required without having access
to the github org.
An example pull request and backport can be seen here:
https://github.com/Mic92/nix-1/pull/4
and here:
https://github.com/Mic92/nix-1/pull/5
To complete the setup the mergify app must be enabled for this repository.
It's already installed in the nixos organization for nixos-hardware and
other repositories.
(cherry picked from commit 80f20fa4cb)
