Tag to be used with the 21.X branches of atlas/athena.
Updates in this tag:
  - Made AnalysisBaseExternals functional on the PPC64 platform.
  - Added some dictionary improvements for detecting upstream changes more reliably that should trigger a dictionary re-generation. Also made the dictionary generation more reliable on MacOS Mojave.
  - Updated AnalysisBaseExternals and AthAnalysisExternals to LCG_94a. This meant updating the version of ROOT and Davix built for AnalysisBaseExternals.
This tag has no release notes.