fix the compiler warning in the header

Fix the compiler warning in a widely used header CbmDigiManager.h since it floods the log during compilation.

requested review from @f.uhlig

assigned to @se.gorbunov

approved this merge request

enabled an automatic merge when the pipeline for 66be7faf succeeds

Dear @f.uhlig, @v.friese, @p.-a.loizeau,

you have been identified as code owner of at least one file which was changed with this merge request.

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added CodeOwners label

merged