chore(deps): update version.camunda to v7.21.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.camunda.bpm:camunda-engine (source)	7.20.0 -> 7.21.0
org.camunda.bpm:camunda-bom (source)	7.20.0 -> 7.21.0

---

Release Notes

camunda/camunda-bpm-platform (org.camunda.bpm:camunda-engine)

### [`v7.21.0`](https://togithub.com/camunda/camunda-bpm-platform/compare/7.20.0...7.21.0) [Compare Source](https://togithub.com/camunda/camunda-bpm-platform/compare/7.20.0...7.21.0)

---

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 these updates 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.