fix(deps): update dependency @astrojs/starlight to v0.21.4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@astrojs/starlight (source)	0.21.3 -> 0.21.4

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Release Notes

withastro/starlight (@​astrojs/starlight)

### [`v0.21.4`](https://togithub.com/withastro/starlight/blob/HEAD/packages/starlight/CHANGELOG.md#0214) [Compare Source](https://togithub.com/withastro/starlight/compare/@astrojs/starlight@0.21.3...@astrojs/starlight@0.21.4) ##### Patch Changes - [#​1703](https://togithub.com/withastro/starlight/pull/1703) [`b26238f2`](https://togithub.com/withastro/starlight/commit/b26238f22990dcf8ba002bea6a50c66f20ad5786) Thanks [@​HiDeoo](https://togithub.com/HiDeoo)! - Fixes aside custom titles rendering for nested asides. - [#​1708](https://togithub.com/withastro/starlight/pull/1708) [`a72cb966`](https://togithub.com/withastro/starlight/commit/a72cb96600798c1fbc7558f8fd24556ca442d312) Thanks [@​HiDeoo](https://togithub.com/HiDeoo)! - Fixes translation issues with Expressive Code when using a default language other than English

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