Update go mod and vendor in client dir to 0.28.0

client/vendor/k8s.io/client-go/discovery/fake/discovery.go

@@ -20,7 +20,7 @@ import (
 	"fmt"
 	"net/http"
 
-	openapi_v2 "github.com/google/gnostic/openapiv2"
+	openapi_v2 "github.com/google/gnostic-models/openapiv2"
 
 	"k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -141,7 +141,10 @@ func (c *FakeDiscovery) ServerVersion() (*version.Info, error) {
 	action := testing.ActionImpl{}
 	action.Verb = "get"
 	action.Resource = schema.GroupVersionResource{Resource: "version"}
-	c.Invokes(action, nil)
+	_, err := c.Invokes(action, nil)
+	if err != nil {
+		return nil, err
+	}
 
 	if c.FakedServerVersion != nil {
 		return c.FakedServerVersion, nil