avoid crash in TrigL2MuonSA due to round-off error

Yohei Yamaguchirequested to merge
yoyamagu/athena:atr-26470 into 22.0

FPE of L2MuonSAMon reported on ATR-26470 is due to round-off error in TrigL2MuonSA package. This MR modify the code to avoid the crash.

ping @anventur and @okumura

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