Fix for FastChainSkeleton.EVGENtoRDO.py after !39019
As part of the changes for the ReSimulation workflow the CfgGetter
method for SimKernel no longer adds it to the AlgSequence automatically,
so this has to be done in the same way as it is for every other algorithm.
(!39019 (merged) was swept to 21.3 as part of !41921 (merged))
This fixes failures seen in the FastChainPileup ART tests. FYI @tcuhadar.