fp_total_failed_votes does not captcher failure if the block is finalized

[code](https://github.com/babylonlabs-io/finality-provider/blob/5f8d43a0b6b676491138eb870e2703f83b74c6db/finality-provider/service/fp_instance.go#L494) returns nil if the block is finalized. The metric should captcher the error