deps: update dependency antsibull-docs to >=2.9,<2.10

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
antsibull-docs (changelog)	>=2.8,<2.9 -> >=2.9,<2.10

---

Release Notes

ansible-community/antsibull-docs (antsibull-docs)

### [`v2.9.0`](https://togithub.com/ansible-community/antsibull-docs/releases/tag/2.9.0) [Compare Source](https://togithub.com/ansible-community/antsibull-docs/compare/2.8.0...2.9.0) ##### Release Summary Maintenance release. ##### Minor Changes - Add support for the antsibull-core v3 ([#​261](https://togithub.com/ansible-community/antsibull-docs/pull/261)).

---

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 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.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by Mend Renovate. View repository job log here.