Update dependency katex to v0.16.21 (forgejo) (#6603)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [katex](https://katex.org) ([source](https://github.com/KaTeX/KaTeX)) | dependencies | patch | [`0.16.20` -> `0.16.21`](https://renovatebot.com/diffs/npm/katex/0.16.20/0.16.21) |

---

### Release Notes

<details>
<summary>KaTeX/KaTeX (katex)</summary>

### [`v0.16.21`](https://github.com/KaTeX/KaTeX/blob/HEAD/CHANGELOG.md#01621-2025-01-17)

[Compare Source](https://github.com/KaTeX/KaTeX/compare/v0.16.20...v0.16.21)

##### Bug Fixes

- escape \htmlData attribute name ([57914ad](https://github.com/KaTeX/KaTeX/commit/57914ad91eff401357f44bf364b136d37eba04f8))

</details>

---

### Configuration

📅 **Schedule**: Branch creation - "* 0-3 * * *" (UTC), Automerge - "* 0-3 * * *" (UTC).

🚦 **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.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOS4xMDYuMCIsInVwZGF0ZWRJblZlciI6IjM5LjEwNi4wIiwidGFyZ2V0QnJhbmNoIjoiZm9yZ2VqbyIsImxhYmVscyI6WyJkZXBlbmRlbmN5LXVwZ3JhZGUiLCJ0ZXN0L25vdC1uZWVkZWQiXX0=-->

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6603
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Renovate Bot <forgejo-renovate-action@forgejo.org>
Co-committed-by: Renovate Bot <forgejo-renovate-action@forgejo.org>