Update dependency postcss to v8.4.39

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss (source)	8.4.38 -> 8.4.39

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Release Notes

postcss/postcss (postcss)

### [`v8.4.39`](https://togithub.com/postcss/postcss/blob/HEAD/CHANGELOG.md#8439) [Compare Source](https://togithub.com/postcss/postcss/compare/8.4.38...8.4.39) - Fixed `CssSyntaxError` types (by [@​romainmenke](https://togithub.com/romainmenke)).

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