Update CSS preprocessors

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
cssnano	5.0.6 -> 5.0.7
postcss (source)	8.3.5 -> 8.3.6

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Release Notes

cssnano/cssnano

### [`v5.0.7`](https://togithub.com/cssnano/cssnano/releases/cssnano@5.0.7) [Compare Source](https://togithub.com/cssnano/cssnano/compare/cssnano@5.0.6...cssnano@5.0.7) #### Bug Fixes - **cssnano**: reduce dependencies by moving from cosmiconfig to lilconfig ([#​1168](https://togithub.com/cssnano/cssnano/issues/1168)) ([506a8232](https://togithub.com/cssnano/cssnano/commit/506a823284191a41752939276f50dbdf75cc8e79))

postcss/postcss

### [`v8.3.6`](https://togithub.com/postcss/postcss/blob/master/CHANGELOG.md#​836) [Compare Source](https://togithub.com/postcss/postcss/compare/8.3.5...8.3.6) - Fixed column in `missed semicolon` error (by [@​Gusted](https://togithub.com/Gusted)).

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