use error.Is to check for nondeterminstic vote error type (#6237) (#6239)

(cherry picked from commit bf8cce83db)

Co-authored-by: Callum Waters <cmwaters19@gmail.com>

consensus/state.go

@@ -1958,7 +1958,7 @@ func (cs *State) tryAddVote(vote *types.Vote, peerID p2p.ID) (bool, error) {
 			)
 
 			return added, err
-		} else if err == types.ErrVoteNonDeterministicSignature {
+		} else if errors.Is(err, types.ErrVoteNonDeterministicSignature) {
 			cs.Logger.Debug("vote has non-deterministic signature", "err", err)
 		} else {
 			// Either