chore: update node engines to next LTS (node 20 / npm 9)

Signed-off-by: John Molakvoæ <skjnldsv@protonmail.com>

package.json

@@ -31,5 +31,9 @@
   },
   "browserslist": [
     "extends @nextcloud/browserslist-config"
-  ]
+  ],
+  "engines": {
+    "node": "^20.0.0",
+    "npm": "^9.0.0"
+  }
 }