Unit tests CI fails when launched via branch or pull request

[IshaanDesai]

The unit tests CI fails when launched via a branch merge or a pull request. An example of the failure: https://github.com/precice/micro-manager/actions/runs/25560350578/job/75030003225. When the failed job is manually triggered, it succeeds.

[Geethapranay1]

hi @IshaanDesai
i found that the workflow expects the OpenMPI cache to always exist, but it can miss on branch/pr runs, so ~/openmpi is missing. I’ve added a fallback to build OpenMPI when the cache isn’t found and will open a pr soon