Fix EndpointSliceController service deletion processing

syncService shouldn't return error if the service doesn't exist which
means it's triggered by service deletion, otherwise the service would be
enqueued repeatedly even its cleanup has been executed successfully.

This patch makes syncService return nil if the error is NotFound when
getting the service, like the other controllers do.

pkg/controller/endpointslice/endpointslice_controller.go

@@ -251,6 +251,8 @@ func (c *Controller) syncService(key string) error {
 	if err != nil {
 		if apierrors.IsNotFound(err) {
 			c.triggerTimeTracker.DeleteService(namespace, name)
+			// The service has been deleted, return nil so that it won't be retried.
+			return nil
 		}
 		return err
 	}

pkg/controller/endpointslice/endpointslice_controller_test.go

@@ -140,9 +140,8 @@ func TestSyncServiceMissing(t *testing.T) {
 
 	err := esController.syncService(fmt.Sprintf("%s/%s", namespace, missingServiceName))
 
-	// Since the service doesn't exist, we should get a not found error
-	assert.NotNil(t, err, "Expected no error syncing service")
-	assert.Equal(t, err.Error(), "service \"notthere\" not found")
+	// nil should be returned when the service doesn't exist
+	assert.Nil(t, err, "Expected no error syncing service")
 
 	// That should mean no client actions were performed
 	assert.Len(t, client.Actions(), 0)