TrigValSteering: fix preExec for transforms

Frank Winklmeierrequested to merge
fwinkl/athena:trigval_prexec into main

Fix a few residual problems introduced in !71057 (merged) that lead to ART test failures:

  • Add missing space when adding --preExec to transform.
  • Fix syntax when multiple flags are being set
  • Disable FPE auditor for release 21 tests

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