fix(deps): update dependency @google-cloud/pubsub to v2.19.4

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@google-cloud/pubsub	2.19.3 -> 2.19.4

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Release Notes

googleapis/nodejs-pubsub

### [`v2.19.4`](https://togithub.com/googleapis/nodejs-pubsub/blob/HEAD/CHANGELOG.md#​2194-httpsgithubcomgoogleapisnodejs-pubsubcomparev2193v2194-2022-05-05) [Compare Source](https://togithub.com/googleapis/nodejs-pubsub/compare/v2.19.3...v2.19.4)

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[tmatsuo]

/gcbrun