Update dependency hexo-theme-next to v8.21.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
hexo-theme-next (source)	8.20.0 -> 8.21.0

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Release Notes

next-theme/hexo-theme-next (hexo-theme-next)

v8.21.0

Compare Source

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Configuration

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