Remove outdated requirement from docs

[offa]

Removes the outdated Jenkins version requirement from docs. It likely wont stay in sync with reality anyway.

Testing done

- only docs -

Submitter checklist

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1. Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
2. Ensure that the pull request title represents the desired changelog entry
3. Please describe what you did
4. Link to relevant issues in GitHub or Jira
5. Link to relevant pull requests, esp. upstream and downstream changes
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue