workflows: less strict memory limits
Uses 256Mi instead of 64Mi which was not enough on some REANA installations such as the the REANA production server at CERN.
GitLab jobs artifacts no longer stored forever as of Monday, November 4th 08:30h. Further information under https://cern.ch/otg0152576
Uses 256Mi instead of 64Mi which was not enough on some REANA installations such as the the REANA production server at CERN.