Bump firebase-admin from 11.5.0 to 12.1.0 in /functions

Bumps [firebase-admin](https://github.com/firebase/firebase-admin-node) from 11.5.0 to 12.1.0.
- [Release notes](https://github.com/firebase/firebase-admin-node/releases)
- [Commits](firebase/firebase-admin-node@v11.5.0...v12.1.0)

---
updated-dependencies:
- dependency-name: firebase-admin
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

functions/package.json

@@ -16,7 +16,7 @@
   },
   "main": "lib/index.js",
   "dependencies": {
-    "firebase-admin": "^11.5.0",
+    "firebase-admin": "^12.1.0",
     "firebase-functions": "^4.9.0"
   },
   "devDependencies": {