chore(deps): update dependency rollup-plugin-postcss to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
rollup-plugin-postcss	3.1.8 -> 4.0.2

---

Release Notes

egoist/rollup-plugin-postcss (rollup-plugin-postcss)

### [`v4.0.2`](https://togithub.com/egoist/rollup-plugin-postcss/releases/tag/v4.0.2) [Compare Source](https://togithub.com/egoist/rollup-plugin-postcss/compare/v4.0.1...v4.0.2) ##### Bug Fixes - prioritize dart-sass over node-sass ([#​402](https://togithub.com/egoist/rollup-plugin-postcss/issues/402)) ([caf3429](https://togithub.com/egoist/rollup-plugin-postcss/commit/caf34295afed324d512841a5a81b229f7749cec8)) ### [`v4.0.1`](https://togithub.com/egoist/rollup-plugin-postcss/releases/tag/v4.0.1) [Compare Source](https://togithub.com/egoist/rollup-plugin-postcss/compare/v4.0.0...v4.0.1) ##### Bug Fixes - update to cssnano 5 ([#​357](https://togithub.com/egoist/rollup-plugin-postcss/issues/357)) ([118253e](https://togithub.com/egoist/rollup-plugin-postcss/commit/118253e402b2c7b99c4504ad45d72f3244a756bd)) ### [`v4.0.0`](https://togithub.com/egoist/rollup-plugin-postcss/releases/tag/v4.0.0) [Compare Source](https://togithub.com/egoist/rollup-plugin-postcss/compare/v3.1.8...v4.0.0) ##### Features - upgrade postcss to 8.x ([ceee1bc](https://togithub.com/egoist/rollup-plugin-postcss/commit/ceee1bc87d91d6c2692e2f44ae2753fa83a0b535)) ##### BREAKING CHANGES - upgrade postcss to 8.x Co-authored-by: Edward Elric Co-authored-by: Ward Peeters

---

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

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

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by Mend Renovate. View repository job log here.