api: return error when `LicenseGet` status is not `200` (#11644)

.changelog/11644.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+api: Improve error message returned by `Operator.LicenseGet`
+```

api/operator.go

@@ -3,6 +3,7 @@ package api
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"strconv"
@@ -338,6 +339,11 @@ func (op *Operator) LicenseGet(q *QueryOptions) (*LicenseReply, *QueryMeta, erro
 		return nil, nil, errors.New("Nomad Enterprise only endpoint")
 	}
 
+	if resp.StatusCode != 200 {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, nil, fmt.Errorf("Unexpected response code: %d (%s)", resp.StatusCode, body)
+	}
+
 	err = json.NewDecoder(resp.Body).Decode(&reply)
 	if err != nil {
 		return nil, nil, err

api/operator_ent_test.go

@@ -0,0 +1,28 @@
+//go:build ent
+// +build ent
+
+package api
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOperator_LicenseGet(t *testing.T) {
+	t.Parallel()
+	c, s, _ := makeACLClient(t, nil, nil)
+	defer s.Stop()
+
+	operator := c.Operator()
+
+	// Make authenticated request.
+	_, _, err := operator.LicenseGet(nil)
+	require.NoError(t, err)
+
+	// Make unauthenticated request.
+	c.SetSecretID("")
+	_, _, err = operator.LicenseGet(nil)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "403")
+}