Prevent branch name collisions in package-update workflow

[Copilot]

The package-update workflow used only github.run_id for branch naming, causing collisions when workflows are re-run or retry.

Changes:

• Branch naming: Include github.run_attempt in branch name pattern: automation/package-update-{run_id}-{run_attempt}
• Concurrency control: Add concurrency.group: package-updates with cancel-in-progress: false to serialize workflow executions
• Traceability: Update PR body to include run attempt number

concurrency:
  group: package-updates
  cancel-in-progress: false

# ...

run: |
  $branch = "automation/package-update-${{ github.run_id }}-${{ github.run_attempt }}"

Each workflow re-run now creates a unique branch and PR instead of failing on push.

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