fix: preserve authorship label delete errors

[haasonsaas]

Summary

• preserve the gh api DELETE exit status before handling absent-label 404s
• keep non-404 label deletion failures from being silently swallowed

Verification

• actionlint .github/workflows/agent-authorship-label.yml
• ruby -c .github/scripts/classify-agent-authorship.rb

[cursor]

PR Summary

Low Risk
Low risk: small bash control-flow change in a GitHub Actions workflow to preserve gh api DELETE exit codes while still ignoring expected 404/not-found cases.

Overview
Fixes delete_label_if_present in agent-authorship-label to preserve the gh api --method DELETE exit status before checking for 404/not-found, ensuring unexpected label deletion failures are surfaced instead of being silently swallowed.

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