chore(deps): update dependency google/cloud-pubsub to v2

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
google/cloud-pubsub	^1.31 -> ^2.0

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Release Notes

googleapis/google-cloud-php-pubsub (google/cloud-pubsub)

### [`v2.1.2`](https://togithub.com/googleapis/google-cloud-php-pubsub/releases/tag/v2.1.2): google/cloud-pubsub v2.1.2 [Compare Source](https://togithub.com/googleapis/google-cloud-php-pubsub/compare/v2.1.1...v2.1.2) ##### Miscellaneous Chores ### [`v2.1.1`](https://togithub.com/googleapis/google-cloud-php-pubsub/releases/tag/v2.1.1): google/cloud-pubsub v2.1.1 [Compare Source](https://togithub.com/googleapis/google-cloud-php-pubsub/compare/v2.1.0...v2.1.1) ##### Miscellaneous Chores ### [`v2.1.0`](https://togithub.com/googleapis/google-cloud-php-pubsub/releases/tag/v2.1.0): google/cloud-pubsub v2.1.0 [Compare Source](https://togithub.com/googleapis/google-cloud-php-pubsub/compare/v2.0.0...v2.1.0) ##### Features - Add custom datetime format for Cloud Storage subscriptions ([#​7181](https://togithub.com/googleapis/google-cloud-php/issues/7181)) ([9d9ecd3](https://togithub.com/googleapis/google-cloud-php/commit/9d9ecd3c2d315df5f2e5bd1262d219088bb29cb4)) ### [`v2.0.0`](https://togithub.com/googleapis/google-cloud-php-pubsub/releases/tag/v2.0.0): google/cloud-pubsub v2.0.0 [Compare Source](https://togithub.com/googleapis/google-cloud-php-pubsub/compare/v1.51.0...v2.0.0) - Release PubSub V2

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