PyPi release job creates separate pipelines for MRs

The PyPi release job will run on MRs, meaning that it creates a separate pipeline when a MR is created.

This is unlike our other CI jobs which only run on MRs and can create a pipeline that allows a release to be published even though the build may have failed on the branch pipeline.

Noticed whilst debugging the packaging of uis/devops/iam/identity-lib#1 (closed).