[master] Enable set_cvmfs_prod_link job after running Python 3 installation

Each set_cvmfs_prod_link job only applies to one Python version as each version is deployed/installed with a different pipeline.

I've ran the task manually for v10.2.8 but it should also be enabled in the CI. I'm not sure it's worth updating the docs as the Python 2 version of the job can probably be removed after the next release. (I'll open a PR for that now)