Update dependency postcss to v8.4.28

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss (source)	8.4.27 -> 8.4.28

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Release Notes

postcss/postcss (postcss)

### [`v8.4.28`](https://togithub.com/postcss/postcss/blob/HEAD/CHANGELOG.md#8428) [Compare Source](https://togithub.com/postcss/postcss/compare/8.4.27...8.4.28) - Fixed `Root.source.end` for better source map (by Romain Menke). - Fixed `Result.root` types when `process()` has no parser.

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