CI: release branches: only publish
Context
This MR is an attempt at removing some tests in the CI for release branches, to accelerate releases.
When we release, first we push a branch such as v7-opam, which will trigger all tests (including opam tests). Once this branch passes all the tests, we push a tag, a branch such as v7-release, and possibly latest-release. Those three cases are protected on tezos/tezos: only release managers can push them. Redoing the same tests as v7-opam just makes the release take more time than necessary and is even a security issue for critical releases.
This MR was not tested yet and I'm not confident in the syntax of the rules clause...
Manually testing the MR
Release managers should try to push a tag and a -release branch with this patch and then delete them.
Reviewers
Edited by Mehdi Bouaziz