Fix the build documentation job
# What does this PR do?

The last two releases were not automatically documented. That's fine for v4.14.0 since we yanked it, and I did a manual update for v4.14.1, but in the future it would be nice to not have to do this!

The first fix is to make sure Transformers is installed from the current checked out branch and not the content of the master branch. The second fix is to run that job on branches with the patter vxxx-release