CI runs of of disc space

Tests in the CI are sometimes running out of disc space, preventing the test run to complete. See https://github.com/ACEsuit/mace/actions/runs/20615258839/job/59206673218?pr=1321 for example for #1321 

<img width="1552" height="1463" alt="Image" src="https://github.com/user-attachments/assets/d46796ac-5733-4836-9b23-ff97209bb5dd" />

