fix(core): Fix property existence checks on AugmentObject (#6842)

Fixes https://community.n8n.io/t/code-node-returns-full-item-object-on-node-all/28823

packages/workflow/test/AugmentObject.test.ts

@@ -570,6 +570,7 @@ describe('AugmentObject', () => {
 
 			augmentedObject.x.z = 5;
 			expect('z' in augmentedObject.x).toBe(true);
+			expect('y' in augmentedObject.x).toBe(true);
 		});
 	});
 });