fix(deps): update dependency mongoose to v6.8.0

Author: renovate-bot

nodejs/nodejs-guestbook/src/backend/package-lock.json

@@ -12,6 +12,6 @@
     "body-parser": "1.20.1",
     "mongodb": "4.12.1",
     "express": "4.18.2",
-    "mongoose": "6.7.5"
+    "mongoose": "6.8.0"
   }
 }