feat: Update package.json to 1.6.0

Author: github-actions[bot]

Assets/MackySoft/MackySoft.SerializeReferenceExtensions/package.json

@@ -2,7 +2,7 @@
 	"name": "com.mackysoft.serializereference-extensions",
 	"displayName": "SerializeReference Extensions",
 	"author": { "name": "MackySoft", "url": "https://github.com/mackysoft" },
-	"version": "1.5.0",
+	"version": "1.6.0",
 	"unity": "2021.3",
 	"description": "Provide popup to specify the type of the field serialized by the [SerializeReference] attribute in the inspector.",
 	"keywords": [ "SerializeReference", "Editor" ],