chore: bump up postcss-loader version to v8 (#5609)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [postcss-loader](https://togithub.com/webpack-contrib/postcss-loader) | [`^7.3.3` -> `^8.0.0`](https://renovatebot.com/diffs/npm/postcss-loader/7.3.3/8.0.0) | [![age](https://developer.mend.io/api/mc/badges/age/npm/postcss-loader/8.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/postcss-loader/8.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/postcss-loader/7.3.3/8.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/postcss-loader/7.3.3/8.0.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>webpack-contrib/postcss-loader (postcss-loader)</summary>

### [`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` ([#&#8203;677](https://togithub.com/webpack-contrib/postcss-loader/issues/677)) ([8dd0315](8dd0315c03))

##### [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 ([#&#8203;667](https://togithub.com/webpack-contrib/postcss-loader/issues/667)) ([8ef0c7e](8ef0c7e5c6))

##### [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 ([#&#8203;658](https://togithub.com/webpack-contrib/postcss-loader/issues/658)) ([e754c3f](e754c3f845))
-   bug with loading configurations after updating `cosmiconfig` to version 8.2 ([684d265](684d265439))

##### [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 ([#&#8203;655](https://togithub.com/webpack-contrib/postcss-loader/issues/655)) ([e8873f4](e8873f46b4))

##### [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](65748ece39))

### [`v7.3.4`](https://togithub.com/webpack-contrib/postcss-loader/blob/HEAD/CHANGELOG.md#734-2023-12-27)

[Compare Source](https://togithub.com/webpack-contrib/postcss-loader/compare/v7.3.3...v7.3.4)

</details>

---

### Configuration

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

---

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packages/frontend/core/package.json

@@ -77,7 +77,7 @@
     "nanoid": "^5.0.3",
     "next-auth": "^4.24.5",
     "next-themes": "^0.2.1",
-    "postcss-loader": "^7.3.3",
+    "postcss-loader": "^8.0.0",
     "react": "18.2.0",
     "react-dom": "18.2.0",
     "react-error-boundary": "^4.0.11",