fix(deps): update dependency @google-cloud/pubsub to v4

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@google-cloud/pubsub	^3.0.0 -> ^4.0.0

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Release Notes

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

### [`v4.0.0`](https://togithub.com/googleapis/nodejs-pubsub/blob/HEAD/CHANGELOG.md#400-2023-08-03) [Compare Source](https://togithub.com/googleapis/nodejs-pubsub/compare/v3.7.3...v4.0.0) ##### ⚠ BREAKING CHANGES - node 12 eos ([#​1774](https://togithub.com/googleapis/nodejs-pubsub/issues/1774)) ([#​1784](https://togithub.com/googleapis/nodejs-pubsub/issues/1784)) ##### Features - Node 12 eos ([#​1774](https://togithub.com/googleapis/nodejs-pubsub/issues/1774)) ([#​1784](https://togithub.com/googleapis/nodejs-pubsub/issues/1784)) ([47b83c1](https://togithub.com/googleapis/nodejs-pubsub/commit/47b83c18c543a7c8763256f79927a7340db56568)) ##### Bug Fixes - Fix typings for IAM methods ([#​1785](https://togithub.com/googleapis/nodejs-pubsub/issues/1785)) ([9a6bdbc](https://togithub.com/googleapis/nodejs-pubsub/commit/9a6bdbce952c81cb1a43fecbce16a3e3ab0f1420))

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