[Bug] Allow periodic update workflow to create a branch

[echoix]

Describe the bug

The periodic update workflow, that runs each month, failed today to create a pull request because of branch naming rules' conventions.

To reproduce

1. See https://github.com/OSGeo/grass/actions/runs/10282750517/job/28455092371

Expected behavior

Relax naming rule conventions to allow the specified branch (by GitHub actions or the person with the PAT used for it).

At the same time, it would be nice to also allow branches starting with revert- followed by a series of numbers corresponding to the PR's number, then followed by another dash. This is what the GitHub interface generates when using the "revert" feature on a merged PR. It is currently unusable for now.

Screenshots

System description

Main at ref 1527322

[nilason]

See related #3308. There are alternatives to be explored.

[echoix]

In either way, we still have some branch name patterns to allow in the repos settings, as we were too strict in June when changing these settings (as we weren't strict enough the last iteration and had unexpected situations where branches were made in the repo out of a fork)