chore(deps): update dependency @google-cloud/firestore to v6.7.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@google-cloud/firestore	6.6.1 -> 6.7.0

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Release Notes

googleapis/nodejs-firestore (@​google-cloud/firestore)

### [`v6.7.0`](https://togithub.com/googleapis/nodejs-firestore/blob/HEAD/CHANGELOG.md#670-2023-07-20) [Compare Source](https://togithub.com/googleapis/nodejs-firestore/compare/v6.6.1...v6.7.0) ##### Features - Expose MultiDb ([#​1857](https://togithub.com/googleapis/nodejs-firestore/issues/1857)) ([1e913db](https://togithub.com/googleapis/nodejs-firestore/commit/1e913dbec97a6ec9339f641e7590ac4d65c7fd17)) ##### Bug Fixes - Resolving issues with MultiDb support ([#​1864](https://togithub.com/googleapis/nodejs-firestore/issues/1864)) ([1af49c1](https://togithub.com/googleapis/nodejs-firestore/commit/1af49c1a852c6a89a7e21a9e749d667b3b728acf))

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