Don't trim path from builder URI

[puerco]

Summary

This PR modifies the identity extraction function to preserve the full path of the attestation identity recorded in the attestation identity.

Trimming the path opens up a vulnerability as an attestation may be validated by a signature triggered from a workflow with the same filename as the expected one.

The identity extraction function is still timing the branch and tag from the identity which we should probably also not do but we handle it in the rule definition so probably we are ok. Further discussion is needed.

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Added a unit test to test the treatment of the signer identity

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 50.62% (+0.1%) from 50.514%
when pulling 4648953 on puerco:check-identities
into 7c50e65 on stacklok:main.