fix(ci): fix Helm chart packaging tag detection

[ian-flores]

Summary

• Fix package-helm job skipping all steps because git describe couldn't find the release tag
• Root cause: semantic-release creates a new commit, so the tag is on a child commit rather than an ancestor
• Solution: checkout main ref and use git tag --sort instead of git describe

Changes

• Add ref: main to checkout step to get latest commit including the release commit
• Replace git describe --tags --abbrev=0 with git tag --sort=-version:refname | head -1

Test plan

• Trigger a release and verify the package-helm job runs successfully
• Verify Helm chart is packaged and pushed to OCI registry
• Verify Helm chart is uploaded to GitHub release