Update dependency cssnano to v5.1.9

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
cssnano	5.1.8 -> 5.1.9

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Release Notes

cssnano/cssnano

### [`v5.1.9`](https://togithub.com/cssnano/cssnano/releases/tag/cssnano%405.1.9) [Compare Source](https://togithub.com/cssnano/cssnano/compare/cssnano@5.1.8...cssnano@5.1.9) #### Bug Fixes - postcss-merge-longhand: preserve more color function fallbacks ([712993cb4a4e0](https://togithub.com/cssnano/cssnano/commit/712993cb4a4e0af6bcf83dd4529b6e825193c367))

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Configuration

📅 Schedule: "every weekday" (UTC).

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

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