build-docker-image: Fix missing && in the instruction to push tag

To avoid issues like [1] [2].

This fixes the workaround instruction triggered to deal with another job which concurrently wrote in the same repository first while this (failing) job [2] tried to write to.

This had the unfortunate effect to break the build [3] so no MR for the new storage release just yet. /me is sad

[1]

11:08:06  + git tag -a swh-lister-20230704.1 -m swh-lister-20230704.1: Bump new release git push origin master swh-lister-20230704.1
11:08:06  fatal: too many params

[2] https://jenkins.softwareheritage.org/job/swh-apps/job/build-docker-image/167/consoleFull

[3] https://jenkins.softwareheritage.org/job/swh-apps/job/build-docker-images/28