Remove 8.6 references for Task Listeners

[aleksander-dytko]

Description

We shouldn't commit to releases for new features in docs. TL functionality won't be delivered with 8.6 but is currently planned for 8.7 (ref).

When should this change go live?

We can release this at any time to fix the commitment and be true on expectations.

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[github-actions]

👋 🤖 ✅ Looks like the changes were ported across versions, nice job! 🎉

You can read more about the versioning within our docs in our documentation guidelines.

[conceptualshark]

Pulled this messaging out of 8.5 as well, thank you for catching this!