Fix Podman compatibility for Prowler image pull

[jorgemarti]

Add docker.io/ registry prefix to PROWLER_IMAGE so Podman can resolve the image name without unqualified-search registries configured.

Checklist

• Pre-commit hooks pass (pre-commit run --all-files)
• No real AWS account IDs or credentials
• Tests pass (pytest / npm test)
• CDK synthesizes (cd infrastructure && npm run build && npx cdk synth)

[carlosinfantes]

Hey Jorge! CI is failing on ruff lint — 11 errors in the test files (unused imports and unused variables).

Quick fix from lambdas/:

ruff check . --fix

This auto-fixes the 7 fixable ones (unused imports). For the 4 F841 (unused result variables), either prefix with _ or remove the assignment:

# Before:
result = analyzer.analyze()

# After (if you don't need the return value):
analyzer.analyze()

I'll push a fix commit to your branch to unblock this. 🤝