chore: make playground private package

Author: sxzz

playground/package.json

@@ -1,8 +1,7 @@
 {
   "name": "unplugin-jsx-string-playground",
   "version": "0.0.0",
-  "license": "MIT",
-  "author": "三咲智子 <sxzz@sxzz.moe>",
+  "private": true,
   "scripts": {
     "dev": "vite",
     "build": "vite build",