acl: fix error type into a string type for serialization issue

acl_endpoint_test.go:507:
        	Error Trace:	acl_endpoint_test.go:507
        	            				retry.go:148
        	            				retry.go:149
        	            				retry.go:103
        	            				acl_endpoint_test.go:504
        	Error:      	Received unexpected error:
        	            	codec.decoder: decodeValue: Cannot decode non-nil codec value into nil error (1 methods)
        	Test:       	TestACLEndpoint_ReplicationStatus

agent/consul/acl_replication.go

@@ -489,7 +489,7 @@ func (s *Server) updateACLReplicationStatusError(errorMsg error) {
 	defer s.aclReplicationStatusLock.Unlock()
 
 	s.aclReplicationStatus.LastError = time.Now().Round(time.Second).UTC()
-	s.aclReplicationStatus.LastErrorMessage = errorMsg
+	s.aclReplicationStatus.LastErrorMessage = errorMsg.Error()
 }
 
 func (s *Server) updateACLReplicationStatusIndex(replicationType structs.ACLReplicationType, index uint64) {

agent/consul/acl_replication_test.go

@@ -1,7 +1,6 @@
 package consul
 
 import (
-	"errors"
 	"fmt"
 	"os"
 	"strconv"
@@ -781,7 +780,7 @@ func TestACLReplication_TokensRedacted(t *testing.T) {
 		require.True(r, status.ReplicatedTokenIndex < token2.CreateIndex, "ReplicatedTokenIndex is not less than the token2s create index")
 		// ensures that token replication is erroring
 		require.True(r, status.LastError.After(minErrorTime), "Replication LastError not after the minErrorTime")
-		require.Equal(r, status.LastErrorMessage, errors.New("failed to retrieve unredacted tokens - replication token in use does not grant acl:write"))
+		require.Equal(r, status.LastErrorMessage, "failed to retrieve unredacted tokens - replication token in use does not grant acl:write")
 	})
 }
 

agent/structs/acl.go

@@ -1269,7 +1269,7 @@ type ACLReplicationStatus struct {
 	ReplicatedTokenIndex uint64
 	LastSuccess          time.Time
 	LastError            time.Time
-	LastErrorMessage     error
+	LastErrorMessage     string
 }
 
 // ACLTokenSetRequest is used for token creation and update operations