fix: update dependency postcss to v8.2.15

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss (source)	8.2.14 -> 8.2.15

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Release Notes

postcss/postcss

### [`v8.2.15`](https://togithub.com/postcss/postcss/blob/master/CHANGELOG.md#​8215) [Compare Source](https://togithub.com/postcss/postcss/compare/8.2.14...8.2.15) - Fixed `list` type definitions (by [@​n19htz](https://togithub.com/n19htz)).

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