Apply Prettier formatting to add_labels.cjs

[Copilot]

Applied standard Prettier formatting rules to pkg/workflow/js/add_labels.cjs after initial refactoring.

Changes:

• Reformatted optional chaining to explicit null checks for consistency
• Adjusted multi-line core.summary.addRaw() call formatting
• Normalized error handling pattern to match project style

Before/After:

// Before
if (labelsResult.error?.includes("No valid labels")) {
  await core.summary.addRaw(`...`).write();
}

// After  
if (labelsResult.error && labelsResult.error.includes("No valid labels")) {
  await core.summary
    .addRaw(
      `...`
    )
    .write();
}

No logic changes - purely formatting alignment with .prettierrc.json configuration.

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