Update for schema changes in cesium-native

Source/CesiumRuntime/Private/Tests/CesiumPropertyTable.spec.cpp

@@ -22,7 +22,7 @@ void FCesiumPropertyTableSpec::Define() {
     model = CesiumGltf::Model();
     pExtension =
         &model.addExtension<CesiumGltf::ExtensionModelExtStructuralMetadata>();
-    pExtension->schema = CesiumGltf::Schema();
+    pExtension->schema.emplace();
     pPropertyTable = &pExtension->propertyTables.emplace_back();
   });
 
@@ -42,7 +42,7 @@ void FCesiumPropertyTableSpec::Define() {
     });
 
     It("constructs invalid instance for missing schema", [this]() {
-      pExtension->schema = std::nullopt;
+      pExtension->schema.reset();
 
       FCesiumPropertyTable propertyTable(model, *pPropertyTable);
       TestEqual(

Source/CesiumRuntime/Private/Tests/CesiumPropertyTexture.spec.cpp

@@ -34,7 +34,7 @@ void FCesiumPropertyTextureSpec::Define() {
   BeforeEach([this]() {
     model = Model();
     pExtension = &model.addExtension<ExtensionModelExtStructuralMetadata>();
-    pExtension->schema = Schema();
+    pExtension->schema.emplace();
     pPropertyTexture = &pExtension->propertyTextures.emplace_back();
   });
 
@@ -53,7 +53,7 @@ void FCesiumPropertyTextureSpec::Define() {
     });
 
     It("constructs invalid instance for missing schema", [this]() {
-      pExtension->schema = std::nullopt;
+      pExtension->schema.reset();
 
       FCesiumPropertyTexture propertyTexture(model, *pPropertyTexture);
       TestEqual(