Tag to be used with the 21.X branches of atlas/athena.
Updates in this tag:
  - Added extra find-modules to make ART's dependencies work from >=LCG_91 versions;
  - Updated HDF5 to 1.10.2, and switched to building it with CMake;
  - Updated KLFitter to v1.2.0;
  - Updated lwtnn to v2.7.1.
This tag has no release notes.