CI for fork PRs

[Borda]

Short Description

enable CI for Forked PRs

PR Checklist

PR Implementer

This is a small checklist for the implementation details of this PR.
If you submit a PR, please look at these points (don't worry about the RisingTeam
and Reviewer workflows, the only purpose of those is to have a compact view of
the steps)

If there are any questions regarding code style or other conventions check out our
summary.

• Implementation
• Docstrings & Typing
• Check __all__ sections and __init__
• Unittests (look at the line coverage of your tests, the goal is 100%!)
• Update notebooks & documentation if necessary
• Pass all tests
• Add the checksum of the last implementation commit to the Changelog

RisingTeam

RisingTeam workflow

• Add pull request to project (optionally delete corresponding project note)
• Assign correct label (if you don't have permission to do this, someone will do it for you.
  Please make sure to communicate the current status of the pr.)
• Does this PR close an Issue? (add closes #IssueNumber at the bottom if
  not already in description)

Reviewer

Reviewer workflow

• Do all tests pass? (Unittests, NotebookTests, Documentation)
• Does the implementation follow rising design conventions?
• Are the tests useful? (!!!) Are additional tests needed?
  Can you think of critical points which should be covered in an additional test?
• Optional: Check coverage locally / Check tests locally if GPU is necessary to execute