Handle Copilot commit identity mismatch in DCO exemptions

[Copilot]

DCO checks were failing for Copilot-generated commits because exemption matching only used commit.author.login, while these commits can surface as Copilot login with bot-style commit author names. This update broadens exemption matching to cover both identity sources used by GitHub payloads.

• Problem

  • Exemption logic relied on commit.author.login only.
  • Copilot-authored commits in PR #856 resolved to Copilot at login-level, so existing copilot-swe-agent[bot] allow-list entries did not apply.

• Workflow updates

  • Extended ALLOWED_USERS with additional Copilot login variants (copilot, Copilot) for compatibility.
  • Updated exemption condition to match against both:
    • commit.author.login
    • commit.commit.author.name (null-safe access chain)

• Behavioral impact

  • Bot/app-authored commits with mismatched login vs commit-author-name no longer fail DCO due to identity normalization differences.
  • Existing DCO enforcement path for non-exempt commits is unchanged.

const githubUsername = commit.author ? commit.author.login : "";
const commitAuthorName = commit?.commit?.author?.name || "";

const isAllowedUser =
  allowedUsers.includes(githubUsername) ||
  allowedUsers.includes(commitAuthorName);

[Copilot]

Pull request overview

Updates the DCO-check GitHub Actions workflow to better exempt Copilot/bot-authored commits when GitHub’s API surfaces differing identities for the same commit.

Changes:

• Extend the ALLOWED_USERS env list with additional Copilot login variants (copilot, Copilot).
• Broaden exemption matching logic beyond commit.author.login by adding a second identity source.

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