[Bug]: Codebase CI is not triggered correctly on PRs coming from forks

[brownbaerchen]

What happened?

After the big CI overhaul #1884, the codebase CI is broken for PRs coming from forks.

Code snippet triggering the error

https://github.com/helmholtz-analytics/heat/actions/runs/26290395781/job/77389130923?pr=2269

Error message or erroneous outcome

Version

main (development branch)

Python version

3.14

PyTorch version

2.11

MPI version

[brownbaerchen]

@JuanPedroGHM, we can use PR #2269 to debug this. You should be able to write to that branch, I think. If not, let me know.