FlavorTagDiscriminants: Fix cppcheck warnings

Johannes Elmsheuserrequested to merge
cherry-pick-d16367e0 into 24.0

This is a backport of fixes from the main to the 24.0 branch for cppcheck warnings in the FlavorTagDiscriminants packages that occurred during the 24.0 to main branch sweep MR !77500 (merged)

(cherry picked from commit d16367e0)

Co-authored-by: Johannes Elmsheuser johannes.elmsheuser@cern.ch

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