FieldManagedObjectTracker: Fix to work with unstructured

Prior to this patch, this fails because the skipnonappliedfieldmanager
uses the `objectcreater` (aka `*runtime.Scheme`) to create a new object
for which it never sets the GVK. In the case of
`*unstructured.Unstructured`, the GVK can not be derived from the object
itself so the operation would subsequently fail [here][0] with an
```
Object 'Kind' is missing in 'unstructured object has no kind'
```

error. Fix this by explicitly setting the GVK in case of unstructured.

[0]: 02eb7d424a/staging/src/k8s.io/apimachinery/pkg/util/managedfields/internal/structuredmerge.go (L98)

Kubernetes-commit: dbdd6a3b4358d91a064de9c0f01d3050e606d553

testing/fixture.go

@@ -19,11 +19,12 @@ package testing
 import (
 	"fmt"
 	"reflect"
-	"sigs.k8s.io/yaml"
 	"sort"
 	"strings"
 	"sync"
 
+	"sigs.k8s.io/yaml"
+
 	jsonpatch "gopkg.in/evanphx/json-patch.v4"
 
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
@@ -702,7 +703,6 @@ func (t *managedFieldObjectTracker) Update(gvr schema.GroupVersionResource, obj
 	}
 	gvk, err := t.mapper().KindFor(gvr)
 	if err != nil {
-		println("kindfor")
 		return err
 	}
 	mgr, err := t.fieldManagerFor(gvk)