merge requests of data packages should be resolved in LbNightlyTools.GitlabUtils.resolveMRs

See https://gitlab.cern.ch/lhcb-core/LbNightlyTools/-/blob/f3681615b38b14e1204bff2fc0024f16ce74c1a3/python/LbNightlyTools/GitlabUtils.py#L190

This requires #85 (closed) to have the resolved MRs taken into account.

/cc @gcorti