Restrict mandatory jobs to branch and merge request pipelines

The mandatory CI job template should be restricting jobs to merge request and branch pipelines. While it was thought that the existing rules: configuration should do so, this does not seem to be the case (https://gitlab.developers.cam.ac.uk/uis/devops/iam/card-database/infrastructure/-/issues/189#note_1236183) and so manually restrict mandatory jobs to those classes of pipeline.