Review Mozilla 1981367: Only ignore older server changeset if local signature is valid

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Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1981367

Description

This patch conflicts with "BB 42730: Patch RemoteSettings to use only local dumps as a data source", specifically services/settings/RemoteSettingsClient.sys.mjs.

I am not super confident on the conflict resolution, therefore I created this ticket.

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