Address typo in new livekit_token_source js client code

[1egoman]

After merging #1224, the ci build broke.

It should have been livekit_token_source_pb, I got the file name wrong 🤦

(Note: not including a new changeset on purpose because I want to re-publish under the old version from the commit that failed)

[changeset-bot]

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Latest commit: b51c101

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