automation: Update nextcloud-collabora Docker tag to v6.4.9.1

This MR contains the following updates:

Package	Update	Change
nextcloud-collabora	patch	6.4.8.4 -> 6.4.9.1

---

Configuration

📅 Schedule: At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻️ Rebasing: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox.

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

---

• If you want to rebase/retry this MR, check this box.

---

This MR has been generated by Renovate Bot. The local configuration can be found in the SI Renovate Bot repository.