message: Ignore signatures from older eras in `SignatureGossipTracker`
diff: @@ -28,6 +28,10 @@ impl SignatureGossipTracker {
  }
  pub(super) fn register_signature(&mut self, signature_id: FinalitySignatureId) {
  + // ignore the signature if it's from an older era
  + if signature_id.era_id < self.era_id {
  + return;
  + }
  // if we registered a signature in a higher era, reset the cache
  if signature_id.era_id > self.era_id {
  self.era_id = signature_id.era_id;
  