nixos/kresd: set .stopIfChanged = false
nixos/kresd: set .stopIfChanged = false

Since version 5.2.0 there's non-empty stop phase:
    ExecStopPost=/usr/bin/env rm -f "/run/knot-resolver/control/%i"
but it's perfectly OK to run that from a different version
(and typically it's no-op anyway).  Real-life example where this helps:
https://github.com/NixOS/nixpkgs/issues/49528#issuecomment-747723198

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