Fail ci-test when project version is different than target branch

E.g. in https://lhcb-nightlies.web.cern.ch/nightly/lhcb-master-mr/3276/ a Gaudi MR was merged into a pinned Gaudi v36r2.

Check can happen for example before https://gitlab.cern.ch/lhcb-core/LbNightlyTools/-/blob/b2d43d2f8c03edfd989055e47d2712fee294b4a0/python/LbNightlyTools/MergeRequestBuilds.py#L323