[Trivial] Silence peer trust messages where we don't record a change

[mrmr1993]

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This PR silences the daemon log messages reporting Decreasing trust for peer $sender_id when the decrease is 0. This removes a source of unnecessary noise in the debug logs.

Fixes https://github.com/MinaProtocol/mina/issues/2569.

[mrmr1993]

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[mrmr1993]

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[mrmr1993]

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