Update module github.com/caddyserver/certmagic to v0.21.6 (forgejo) (#6510)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [github.com/caddyserver/certmagic](https://github.com/caddyserver/certmagic) | require | patch | `v0.21.5` -> `v0.21.6` |

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### Release Notes

<details>
<summary>caddyserver/certmagic (github.com/caddyserver/certmagic)</summary>

### [`v0.21.6`](https://github.com/caddyserver/certmagic/releases/tag/v0.21.6)

[Compare Source](https://github.com/caddyserver/certmagic/compare/v0.21.5...v0.21.6)

Minor patch for ARI handshake maintenance.

#### What's Changed

- Fix typos by [@&#8203;deining](https://github.com/deining) in https://github.com/caddyserver/certmagic/pull/324
- Replace interface{} with any by [@&#8203;deining](https://github.com/deining) in https://github.com/caddyserver/certmagic/pull/325
- ari: Only check if cert is not expired, and use proper context by [@&#8203;mholt](https://github.com/mholt) in https://github.com/caddyserver/certmagic/pull/328

#### New Contributors

- [@&#8203;deining](https://github.com/deining) made their first contribution in https://github.com/caddyserver/certmagic/pull/324

**Full Changelog**: https://github.com/caddyserver/certmagic/compare/v0.21.5...v0.21.6

</details>

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