Initial attempt to get file hashes when git checkout is done

[pljones]

Short description of changes

Hopefully a fix for:

Error: The template is not valid. .github/workflows/autobuild.yml (Line: 326, Col: 37): hashFiles('.github/workflows/autobuild.yml, .github/autobuild/mac.sh, mac/deploy_mac.sh') failed. Fail to hash files under directory '/Users/runner/work/jamulus/jamulus'

... but Claude Haiku thinks it's intermittent. GPT 5 mini came up with roughly this idea. Ideally it would be done once the check out is confirmed to have completed successfully.

CHANGELOG: SKIP

Context: Fixes an issue?

Yes

Does this change need documentation? What needs to be documented and how?

No

Status of this Pull Request

Waiting a clean build through Github.

What is missing until this pull request can be merged?

Hopefully doesn't break anything...

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

[pljones]

Well that was a total failure. Hm. I've no idea what I'm doing, to be honest...