Tag to be used with the 21.X branches of atlas/athena.
Updates in this tag:
- Updated to using externals from LCG_97a in AnalysisBaseExternals and AthAnalysisExternals. Including:
* Boost 1.70.0 --> 1.72.0;
* fjcontrib 1.041 --> 1.044;
* GoogleTest <unknown/untagged> --> 1.10.0;
* HDF5 1.10.3 --> 1.10.5;
* LHAPDF 6.2.3 --> 6.3.0;
* setuptools 41.0.0 --> 44.1.0;
* ROOT 6.18/04 --> 6.20/06;
* TBB 2019_U7 --> 2020_U1;
* XRootD 4.10.0 --> 4.12.2;
* nlohmann_json 3.5.0 --> 3.6.1;