Always open a pull request against develop. Add the backport-master label.
gh pr create --base develop --label backport-masterDo not open a pull request against master. When a pull request on develop
merges, Mergify opens the backport to master (see .mergify.yml). A pull
request on master skips develop, and someone must backport it by hand.
Do not add backport-master to a pull request that targets master. Mergify
then opens a duplicate backport to master.