fix(ci): trigger required checks on automated PRs

[jdalton]

Summary

• Pushes made with GITHUB_TOKEN don't trigger other workflows (this is a GitHub limitation by design)
• Required CI and enterprise audit checks get stuck at "Waiting for workflow to run" on automated PRs created by the weekly update workflow
• Add a close/reopen step after PR creation to generate a pull_request.reopened event, which triggers the required workflows

Test plan

• Run the weekly update workflow via workflow_dispatch and verify CI checks trigger on the created PR
• Confirm the PR is in an open (not closed) state after the close/reopen cycle