OCPBUGS-81751: Fix GatewayClass update conflict in markTestDone

Add retry logic to markTestDone to handle optimistic locking conflicts
when updating GatewayClass annotations. The CIO actively manages the
GatewayClass (updating conditions, status, finalizers) which can cause
409 Conflict errors when tests try to update annotations.

Using RetryOnConflict ensures the test automatically retries with the
latest resourceVersion when concurrent updates occur.

Fixes flake:
  Operation cannot be fulfilled on gatewayclasses.gateway.networking.k8s.io
  "openshift-default": the object has been modified; please apply your
  changes to the latest version and try again

https://redhat.atlassian.net/browse/OCPBUGS-81751

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gcs278

test/extended/router/gatewayapicontroller.go

@@ -34,6 +34,7 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/apiserver/pkg/storage/names"
+	"k8s.io/client-go/util/retry"
 	gatewayapiv1 "sigs.k8s.io/gateway-api/apis/v1"
 )
 
@@ -1101,14 +1102,19 @@ func annotationKeyForTest(testName string) string {
 // These annotations are used to determine whether it is safe to clean up the
 // gatewayclass and other shared resources.
 func markTestDone(oc *exutil.CLI, testName string) {
-	gwc, err := oc.AdminGatewayApiClient().GatewayV1().GatewayClasses().Get(context.Background(), gatewayClassName, metav1.GetOptions{})
-	o.Expect(err).NotTo(o.HaveOccurred())
+	err := retry.RetryOnConflict(retry.DefaultRetry, func() error {
+		gwc, err := oc.AdminGatewayApiClient().GatewayV1().GatewayClasses().Get(context.Background(), gatewayClassName, metav1.GetOptions{})
+		if err != nil {
+			return err
+		}
 
-	if gwc.Annotations == nil {
-		gwc.Annotations = map[string]string{}
-	}
-	gwc.Annotations[annotationKeyForTest(testName)] = ""
-	_, err = oc.AdminGatewayApiClient().GatewayV1().GatewayClasses().Update(context.Background(), gwc, metav1.UpdateOptions{})
+		if gwc.Annotations == nil {
+			gwc.Annotations = map[string]string{}
+		}
+		gwc.Annotations[annotationKeyForTest(testName)] = ""
+		_, err = oc.AdminGatewayApiClient().GatewayV1().GatewayClasses().Update(context.Background(), gwc, metav1.UpdateOptions{})
+		return err
+	})
 	o.Expect(err).NotTo(o.HaveOccurred())
 }