fix: upgrade firebase-admin from 12.3.0 to 12.6.0

Snyk has created this PR to upgrade firebase-admin from 12.3.0 to 12.6.0.

See this package in npm:
firebase-admin

See this project in Snyk:
https://app.snyk.io/org/saileshbro-sv8/project/25a027d2-c1ab-4c07-8a51-071d3c26ca6d?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

functions/package-lock.json

@@ -13,7 +13,7 @@
     "node": "10"
   },
   "dependencies": {
-    "firebase-admin": "^12.3.0",
+    "firebase-admin": "^12.6.0",
     "firebase-functions": "^6.1.0"
   },
   "devDependencies": {