fix(deps): update dependency postcss-loader to v8

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss-loader	7.3.4 -> 8.1.1

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Release Notes

webpack-contrib/postcss-loader (postcss-loader)

### [`v8.1.1`](https://togithub.com/webpack-contrib/postcss-loader/blob/HEAD/CHANGELOG.md#811-2024-02-28) [Compare Source](https://togithub.com/webpack-contrib/postcss-loader/compare/v8.1.0...v8.1.1) ### [`v8.1.0`](https://togithub.com/webpack-contrib/postcss-loader/blob/HEAD/CHANGELOG.md#810-2024-01-30) [Compare Source](https://togithub.com/webpack-contrib/postcss-loader/compare/v8.0.0...v8.1.0) ##### Features - add `@rspack/core` as an optional peer dependency ([#​679](https://togithub.com/webpack-contrib/postcss-loader/issues/679)) ([512e4c3](https://togithub.com/webpack-contrib/postcss-loader/commit/512e4c33a6072534008c0eefc481139f58effbdf)) ### [`v8.0.0`](https://togithub.com/webpack-contrib/postcss-loader/blob/HEAD/CHANGELOG.md#800-2024-01-16) [Compare Source](https://togithub.com/webpack-contrib/postcss-loader/compare/v7.3.4...v8.0.0) ##### ⚠ BREAKING CHANGES - minimum supported Node.js version is `18.12.0` ([#​677](https://togithub.com/webpack-contrib/postcss-loader/issues/677)) ([8dd0315](https://togithub.com/webpack-contrib/postcss-loader/commit/8dd0315c03e0f608b6a9a4c6a58e9e7a64775e56)) ##### [7.3.4](https://togithub.com/webpack-contrib/postcss-loader/compare/v7.3.3...v7.3.4) (2023-12-27) ##### Bug Fixes - do not crash if pkg.(d|devD)ependencies unset ([#​667](https://togithub.com/webpack-contrib/postcss-loader/issues/667)) ([8ef0c7e](https://togithub.com/webpack-contrib/postcss-loader/commit/8ef0c7e5c6c4eb76073b4ea92306fc399014e462)) ##### [7.3.3](https://togithub.com/webpack-contrib/postcss-loader/compare/v7.3.2...v7.3.3) (2023-06-10) ##### Bug Fixes - **perf:** avoid using `klona` for postcss options ([#​658](https://togithub.com/webpack-contrib/postcss-loader/issues/658)) ([e754c3f](https://togithub.com/webpack-contrib/postcss-loader/commit/e754c3f8451a09ea633674af90fb3b6b1c073460)) - bug with loading configurations after updating `cosmiconfig` to version 8.2 ([684d265](https://togithub.com/webpack-contrib/postcss-loader/commit/684d2654393d225bbbcc443ffc9494ab54fe8112)) ##### [7.3.2](https://togithub.com/webpack-contrib/postcss-loader/compare/v7.3.1...v7.3.2) (2023-05-28) ##### Bug Fixes - use `cause` to keep original errors and warnings ([#​655](https://togithub.com/webpack-contrib/postcss-loader/issues/655)) ([e8873f4](https://togithub.com/webpack-contrib/postcss-loader/commit/e8873f46b4ac3cf94d854d8c20f0d0a444309eb6)) ##### [7.3.1](https://togithub.com/webpack-contrib/postcss-loader/compare/v7.3.0...v7.3.1) (2023-05-26) ##### Bug Fixes - warning and error serialization ([65748ec](https://togithub.com/webpack-contrib/postcss-loader/commit/65748ece396d0b38713783495d8a64f128d3992b))

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