Update dependency firebase-functions to v4.8.1

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
firebase-functions	4.8.0 -> 4.8.1

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Release Notes

firebase/firebase-functions (firebase-functions)

### [`v4.8.1`](https://togithub.com/firebase/firebase-functions/compare/v4.8.0...536f8debeec4552264d8f6a7a12f10293c42aba9) [Compare Source](https://togithub.com/firebase/firebase-functions/compare/v4.8.0...v4.8.1)

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