chore(greenhouse): add long SHA to Greenhouse release to fix image scan error and report failing steps

[ArtieReus]

Summary

This PR updates the Greenhouse release configuration to include the full Git SHA (type=raw,value=${{ github.sha }}).
This change addresses a runtime error during image scanning by explicitly including the long SHA, we ensure the image reference is correct and scannable, resolving the scan initialization failure. Adds Slack notification with the name of the failing job for easier debugging.

Changes Made

• Add long SHA to Greenhouse release
• Adds Slack notification with the name of the failing job the the release workflow of greenhouse and supernova.

Related Issues

• https://github.com/cloudoperators/juno/actions/runs/16315212549/job/46079613253

Checklist

• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have made corresponding changes to the documentation (if applicable).
• My changes generate no new warnings or errors.
• I have created a changeset for my changes.

PR Manifesto

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[changeset-bot]

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Latest commit: 9d2bdf9

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[hodanoori]

lgtm