Only run GitHub actions from jenkinsci org

[MarkEWaite]

Only run GitHub actions from jenkinsci org

No need to deploy site on forks

Testing done

Technique is working for jenkins.io and for several other repositories.

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

[basil]

I fixed up a few others:

./jellydoc-maven-plugin/.github/workflows/site.yml
./jelly/.github/workflows/site.yml
./license-maven-plugin/.github/workflows/site.yml
./maven-hpi-plugin/.github/workflows/site.yml
./stapler-maven-plugin/.github/workflows/site.yml

[MarkEWaite]

Thanks!