Bump to go-witness version with improved SBOMs and added testing

[jkjell]

What this PR does / why we need it

Bump to go-witness version with improved SBOMs and added testing

Requires https://github.com/in-toto/go-witness/pull/281

Acceptance Criteria Met

• [x] Docs changes if needed
• [x] Testing changes if needed
• [ ] All workflow checks passing (automatically enforced)
• [ ] All review conversations resolved (automatically enforced)
• [x] DCO Sign-off

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