Some tests fail in CI due to no space left on GitHub runners

[jpraynaud]

Why

We have noticed that all the Rust unit tests were failing on Ubuntu 24 in the CI for a few days:

• https://github.com/input-output-hk/mithril/actions/runs/19372559970/job/55431832950?pr=2765#step:4:45
• https://github.com/input-output-hk/mithril/actions/runs/19371868144/job/55429554664#step:4:88
• https://github.com/input-output-hk/mithril/actions/runs/19423053079/job/55564168732

It appears that the problem is due to GitHub runners being out of disk space:

Unhandled exception. System.IO.IOException: No space left on device : '/home/runner/actions-runner/cached/_diag/Worker_20251117-080311-utc.log'

What

Investigate and fix the problem that leads to out of space errors on the GitHub runners

How

• Investigate the source of the problem
• Create a fix