chore(v4.6.x): release 4.6.8

[shaka-bot]

🤖 I have created a release beep boop

4.6.8 (2024-01-11)

Bug Fixes

• Ads: Fix muting/unmuting ads won't affect video and vice versa (#6073) (71f7c57)
• fix handling of multiple CC tracks (#6076) (215b204)
• HLS: getPlayheadTimeAsDate() differs from X-EXT-PROGRAM-DATE-TIME (#6059) (7d41ddc)
• offline: Fix server certificate error when trying to delete stored content (#6080) (fd770ad)
• UI: Fix replay button when the post-roll is running using CS (#6072) (6c8b700)

Performance Improvements

• Improve performance of addThumbnailsTrack (#6067) (8d29cff)
• WebVTT: Improve parsing time for unstyled payloads (#6066) (5740367)

Reverts

• Install by default shaka.polyfill.PatchedMediaKeysApple when there is no unprefixed EME support (#6068) (8747403)

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[shaka-bot]

🤖 Release is at https://github.com/shaka-project/shaka-player/releases/tag/v4.6.8 🌻