Fix cosign sign image reference (lowercase OCI ref)

[Devathmaj]

Cosign fails parsing \ghcr.io/Devathmaj/VoucherBot@sha256:...\ because OCI/image references are case-sensitive and must be lowercase. Lowercase \IMAGE_NAME\ before signing.

Summary by CodeRabbit

• Bug Fixes
  • Improved Docker image publishing reliability by normalizing image names before signing.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 47829965-d080-4707-8a3c-d7446a3a5d60

📥 Commits

Reviewing files that changed from the base of the PR and between d200bad and 71365c4.

📒 Files selected for processing (1)

• .github/workflows/release.yml

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📝 Walkthrough

Walkthrough

The release workflow now lowercases IMAGE_NAME and exports the normalized value to GITHUB_ENV before Docker image signing.

Changes

Release Image Normalization

Layer / File(s)	Summary
Normalize IMAGE_NAME .github/workflows/release.yml	The workflow lowercases IMAGE_NAME and persists the normalized value for subsequent steps.

Estimated code review effort: 1 (Trivial) | ~5 minutes

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch security-hardening

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