Update dependency firebase-functions to v4.9.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
firebase-functions	4.8.1 -> 4.9.0

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Release Notes

firebase/firebase-functions (firebase-functions)

### [`v4.9.0`](https://togithub.com/firebase/firebase-functions/releases/tag/v4.9.0) [Compare Source](https://togithub.com/firebase/firebase-functions/compare/v4.8.2...v4.9.0) - Add new 2nd gen Firestore auth context triggers. ([#​1519](https://togithub.com/firebase/firebase-functions/issues/1519)) ### [`v4.8.2`](https://togithub.com/firebase/firebase-functions/releases/tag/v4.8.2) [Compare Source](https://togithub.com/firebase/firebase-functions/compare/v4.8.1...v4.8.2) Fix bug with CORS options for an array of one string ([#​1544](https://togithub.com/firebase/firebase-functions/issues/1544))

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