Tests failing due to hashFiles function

[nichollsh]

The GitHub tests are now, suddenly, failing because of an error:

Error: The template is not valid. .github/workflows/tests.yaml (Line: 96, Col: 16): hashFiles('pyproject.toml') failed. Fail to hash files under directory '/Users/runner/work/PROTEUS/PROTEUS'

I don't think this is our fault. See:

• issue Post cache failed with "The template is not valid. hashFiles('**/Makefile') failed." on MacOs actions/runner#449 (comment)
• discussion https://github.com/orgs/community/discussions/180160
• issue Fail to hash files actions/runner-images#13341

@FormingWorlds/proteus-developer

[nichollsh]

It is suggested that using the checkout@v6 and setup-python@v6 versions can mitigate the problem. I have tried this in the br/inference branch, which seems to fix the problem.

[nichollsh]

Update: this only fixes the problem when the workflow is re-run for the first time. Broken again.