Support SHA-256 git hashes in reference checks

[James Frost (jfrost-mo)]

PR Summary

Git 3.0 will be defaulting to SHA-256, so will have longer (64 character) object IDs.

This PR has not exhaustively reviewed support for SHA-256, only fixed an issue I spotted when making another change, and a couple others I found by grepping for the {40} regex pattern.

Sci/Tech Reviewer:
Code Reviewer:

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• This change has been tested appropriately (please describe)

I have successfully cloned a SHA-256 repository (hosted on a local webserver) with this script. Both hashes and branches as refs worked, though hashes required hacking clone_repo as directly fetching a commit is not supported by the dumb HTTP transport. This would not be an issue on a proper git host.

I have also verified that existing checks for SHA-1 hashes remain working.

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• Code quality standards have been met
• Tests are adequate and have passed
• Security considerations have been addressed
• Performance impact is acceptable