ci-test jobs ignore project target version in some cases

The build https://lhcb-nightlies.web.cern.ch/nightly/lhcb-master-mr/build/740/ failed because it used a commit from Detector branch master, instead of v0-patches as requested by the configuration of lhcb-master.

In the related logs in Jenkins (https://jenkins-lhcb-nightlies.web.cern.ch/job/nightly-builds/job/main/4286/console) I found

2020-04-29 23:06:16,775:DEBUG   : getLastCommit invoked with (('lhcb/Detector', '2020-04-23T09:43:33', u'master'), {})
... 
2020-04-29 23:06:16,880:DEBUG   : https://gitlab.cern.ch:443 "GET //api/v4/projects/lhcb%2FDetector HTTP/1.1" 200 2664
2020-04-29 23:06:17,539:DEBUG   : https://gitlab.cern.ch:443 "GET //api/v4/projects/59993/repository/commits?until=2020-04-23T09%3A43%3A33&ref_name=master HTTP/1.1" 200 10762
2020-04-29 23:06:17,541:DEBUG   : Setting checkout for 'Detector' to be 'a5beb97c83dcbadc608229645c3ab37e5ff37776'

When the ci-test is invoked with --merge, everything is OK