Gate PR creation on commit detection in package-update workflow

[Copilot]

Addresses feedback from PR #794 where the workflow would fail when no package updates are available. The commit step exits successfully when git diff --cached --quiet is true, but the PR creation step still runs with if: success() and fails due to the missing remote branch.

Changes:

• Add step output has-changes to propagate change detection state
• Set has-changes=false when no staged changes detected, has-changes=true after successful push
• Gate PR creation on steps.commit.outputs.has-changes == 'true' instead of success()

- name: Create branch, commit, push
  id: commit
  run: |
    if (git diff --cached --quiet) {
      echo "has-changes=false" >> $env:GITHUB_OUTPUT
      exit 0
    }
    git commit -m "..."
    git push ...
    echo "has-changes=true" >> $env:GITHUB_OUTPUT

- name: Open PR with gh
  if: steps.commit.outputs.has-changes == 'true'

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