Update unit tests and feature name

Update the unit tests to include checks for incorrect APIGroup type in
PVC DataSource and change the name of the feature gate to be more clear:
s/VolumeDataSource/VolumePVCDataSource/

pkg/apis/core/validation/validation_test.go

@@ -13311,7 +13311,7 @@ func testDataSourceInSpec(name string, kind string, apiGroup string) *core.Persi
 	return &dataSourceInSpec
 }
 
-func TestAlphaVolumeDataSource(t *testing.T) {
+func TestAlphaVolumePVCDataSource(t *testing.T) {
 	successTestCases := []core.PersistentVolumeClaimSpec{
 		*testDataSourceInSpec("test_snapshot", "VolumeSnapshot", "snapshot.storage.k8s.io"),
 		*testDataSourceInSpec("test_pvc", "PersistentVolumeClaim", ""),