Peer dependency for firebase-admin 13

[Matt-Jennings-GitHub]

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Description

Resolve package not compatible with firebase-admin 13

Previously, firebase-admin 13 was not supported in peer dependencies. Original peer deps:

"peerDependencies": {
    "firebase-admin": "^8.0.0 || ^9.0.0 || ^10.0.0 || ^11.0.0 || ^12.0.0",
    "firebase-functions": ">=4.9.0",
    "jest": ">=28.0.0"
  },

firebase-functions-test should work with latest version of firebase-admin. Tests passing.