fix(deps): update module github.com/livekit/protocol to v1.21.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
github.com/livekit/protocol	v1.20.1 -> v1.21.0

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Release Notes

livekit/protocol (github.com/livekit/protocol)

### [`v1.21.0`](https://redirect.github.com/livekit/protocol/compare/v1.20.1...v1.21.0) [Compare Source](https://redirect.github.com/livekit/protocol/compare/v1.20.1...v1.21.0)

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