Disable pipeline runs as triggered by push

As we saw during the PoC gitlab currently triggers a pipeline run when a user pushes: https://gitlab.archlinux.org/packaging-buildbtw-dev/packages/fastfetch/-/commit/bf1c68ad927ac8a31f7fa6f4046a9ad2aef1eaa7

We should disable this because it triggers a run that fails and since the push by user is the cause of the pipeline run they will also get a notification mail for the failed run.

Afterwards notifications for the Gitlab group can be enabled again. 🤗