Draft: Trigger baseline only on tag push

This change is backed by the maintainers workflow change: instead of
merging multiple MRs at a time behind the scenes, merge each MR separately
using the "merge" button.

With that, only run the baseline pipeline when a tag is submitted to prevent
multiple pipelines triggers that are canceled later when a new merge is
performed.

Signed-off-by: Bruno Meneguele bmeneg@redhat.com