chore(deps): update devdependency postcss to v8.4.7

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss (source)	8.4.6 -> 8.4.7

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Release Notes

postcss/postcss

### [`v8.4.7`](https://togithub.com/postcss/postcss/blob/HEAD/CHANGELOG.md#​847) [Compare Source](https://togithub.com/postcss/postcss/compare/8.4.6...8.4.7) - Fixed `Node#warn()` type (by Masafumi Koba). - Fixed comment removal in values after `,`.

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