Release notes for release/21.0.126

The release release/21.0.126 was built from the tag nightly/21.0/2021-04-28T2123

This is the list of merge requests that were included since the previous release release/21.0.125:

• !42991 : Reporting ReSim events to the jobReport (ATLASJT-417)

Link to the full diff between release/21.0.126 and release/21.0.125 is available at https://gitlab.cern.ch/atlas/athena/compare/release/21.0.125...release/21.0.126