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

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@google-cloud/text-to-speech	^3.0.0 -> ^4.0.0

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Release Notes

googleapis/nodejs-text-to-speech

v4.0.0

Compare Source

⚠ BREAKING CHANGES

• update library to use Node 12 (#​604)

Features

• Consolidate task details into service API and add orchestration result details (74f7cfb)
• promote CustomVoiceParams to v1 (#​591) (fe647dc)

Build System

• update library to use Node 12 (#​604) (4395d56)

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Configuration

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