Update CI tags to consistently use 9.X runners

Update to CI tag for selecting consistent GitLab runners (9.X)

See https://cern.service-now.com/service-portal/view-outage.do?n=OTG0043129 for more details about recent changes.

Also, https://cern.service-now.com/service-portal/view-outage.do?n=OTG0044665 describing the new 11.X runners being used

There seem to still be some issues with the new 11.X runners, see for example

https://gitlab.cern.ch/atlas-physics/higgs/hww/HWWAnalysisCode/issues/12

so for now use 9.X runners.