Fix JENKINS-69719: Fetch PR data from target repo

[astos-marcb]

Jenkins token permissions potentially invalid to access source repo.
This is the cause of issue JENKINS-69719.

All required Gitea Pull Request data can be accessed via target repo.
Replace access to potentially inaccessible source repository by references in target repository Pull Request head.

Testing done

The change affects token/credential permission scope on the Gitea server.
With the changed source for data access, the MultiBranchPipeline scan completes.

Jenkins can pull/checkout (moving) head of pull request.
Resolution to commit hash is done independently in body of GiteaSCMFileSystem constructor.

Submitter checklist

Beta Give feedback

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

[astos-marcb]

@justusbunsi any reservations on applying the change (apart form the obvious copy&pase style)?
And a possible timeline (with it) on 1.4.6? This change may affect some decisions on Gitea/Jenkins use here. 😄

[justusbunsi]

@justusbunsi any reservations on applying the change (apart form the obvious copy&pase style)? And a possible timeline (with it) on 1.4.6? This change may affect some decisions on Gitea/Jenkins use here. 😄

@astos-marcb To be honest, I received the "review requested" notification back then and simply missed acting upon it after reading it. 🙏 Thank you for your ping.

I've no reservation on applying your changes. I was able to reproduce the mentioned issue with a non-admin user. Reviewed and tested your changes now. Well spotted. Thanks for your contribution. Even with such a delay on my side. Sorry for that.

Regarding release timeline: There is #60 also awaiting my review. I'm going to review that PR after merging yours. With #60 also merged, we should be ready to release 1.4.6. We'll see if I need to bump the dependencies for a successful release. Missed quite a few versions in the meantime. 😅