Some doc branches fail to build an ISO because the base branch of master is "testing" after a major release

Until today our master branch had “testing” in config/base_branch. This worked for a while but about 10 days ago, branches based on master started failing to build ISO images. An instance of that problem was reported by sajolida.

I’ve just reset the base branch there to “stable” and I hope it’ll fix the problem for doc branches that have current master merged in (so they have my commit).

anonym, can you please:

1. check that it fixes the problem (I’ve just merged this updated master branch into doc/9849-sponsor-deliverable-roles and pushed it)
2. ensure we always reset the base branch to “stable” on the master branch at some well chosen point in the release process

I think this won’t happen after a bugfix release, so setting target version to our next major release (3.5).

Related issues

• Related to #14459 (closed)
• Blocks #11355

Original created by @intrigeri on 14857 (Redmine)