fix(deps): update all non-major

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@google-cloud/firestore	^4.15.0 -> ^4.15.1
firebase-functions	^3.15.4 -> ^3.15.5

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Release Notes

googleapis/nodejs-firestore

### [`v4.15.1`](https://togithub.com/googleapis/nodejs-firestore/blob/master/CHANGELOG.md#​4151-httpswwwgithubcomgoogleapisnodejs-firestorecomparev4150v4151-2021-09-03) [Compare Source](https://togithub.com/googleapis/nodejs-firestore/compare/v4.15.0...v4.15.1)

firebase/firebase-functions

### [`v3.15.5`](https://togithub.com/firebase/firebase-functions/releases/v3.15.5) [Compare Source](https://togithub.com/firebase/firebase-functions/compare/v3.15.4...v3.15.5) - Make the minInstances feature public.

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