Update postcss (forgejo) (#6562)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [postcss](https://postcss.org/) ([source](https://github.com/postcss/postcss)) | dependencies | minor | [`8.4.49` -> `8.5.1`](https://renovatebot.com/diffs/npm/postcss/8.4.49/8.5.1) |
| [postcss-html](https://github.com/ota-meshi/postcss-html) | devDependencies | minor | [`1.7.0` -> `1.8.0`](https://renovatebot.com/diffs/npm/postcss-html/1.7.0/1.8.0) |

---

### Release Notes

<details>
<summary>postcss/postcss (postcss)</summary>

### [`v8.5.1`](https://github.com/postcss/postcss/blob/HEAD/CHANGELOG.md#851)

[Compare Source](https://github.com/postcss/postcss/compare/8.5.0...8.5.1)

- Fixed backwards compatibility for complex cases (by [@&#8203;romainmenke](https://github.com/romainmenke)).

### [`v8.5.0`](https://github.com/postcss/postcss/releases/tag/8.5.0): 8.5 “Duke Alloces”

[Compare Source](https://github.com/postcss/postcss/compare/8.4.49...8.5.0)

<img src="https://github.com/user-attachments/assets/6ef654a0-d675-4ba0-a670-e28ef27062f5" align="right" width="200" height="200" alt="President Alloces seal">

PostCSS 8.5 brought API to work better with non-CSS sources like HTML, Vue.js/Svelte sources or CSS-in-JS.

[@&#8203;romainmenke](https://github.com/romainmenke) during [his work](https://github.com/postcss/postcss/issues/1995) on [Stylelint](https://stylelint.io) added `Input#document` in additional to `Input#css`.

```js
root.source.input.document //=> "<p>Hello</p>
// <style>
// p {
// color: green;
// }
// </style>"
root.source.input.css //=> "p {
// color: green;
// }"

```

#### Thanks to Sponsors

This release was possible thanks to our community.

If your company wants to support the sustainability of front-end infrastructure or wants to give some love to PostCSS, you can join our supporters by:

- [**Tidelift**](https://tidelift.com/) with a Spotify-like subscription model supporting all projects from your lock file.
- Direct donations at [**GitHub Sponsors**](https://github.com/sponsors/ai) or [**Open Collective**](https://opencollective.com/postcss#section-contributors).

</details>

<details>
<summary>ota-meshi/postcss-html (postcss-html)</summary>

### [`v1.8.0`](https://github.com/ota-meshi/postcss-html/releases/tag/v1.8.0)

[Compare Source](https://github.com/ota-meshi/postcss-html/compare/v1.7.0...v1.8.0)

#### What's Changed

- update to latest PostCSS by [@&#8203;romainmenke](https://github.com/romainmenke) in https://github.com/ota-meshi/postcss-html/pull/134

**Full Changelog**: https://github.com/ota-meshi/postcss-html/compare/v1.7.0...v1.8.0

</details>

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Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6562
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Renovate Bot <forgejo-renovate-action@forgejo.org>
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