chore: refresh Hacktoberfest 2026 prep tracker

[github-actions]

Automated daily refresh of the Hacktoberfest 2026 open-PR cleanup tracker (docs/hacktober_2026_prep.md): ticks off any tracked pull request that has since been merged/closed and rewrites the Automated statistics section.

This PR is updated in place by the hacktoberfest_prep workflow, so it always reflects the latest scheduled run. Merge it whenever you want to capture the current snapshot.

[cclauss]

@priya-sundaram-dev Please create a PR for the following:

We currently have 107 open issues, not 621.

Please enhance these statistics by adding:
Number of days until Hacktoberfest: x
Average number of issues we should close per day until Hacktoberfest: x
Average number of pull requests we should merge or close until Hacktoberfest: x

[priya-sundaram-dev]

Fixed in #15233 — the "Open issues" line now reads 107, not 621. The search is:issue/is:pr qualifiers were returning the PR pool for both queries; I switched to deterministic counts (open PRs from the pulls Link: rel="last" page number, open issues = repo open_issues_count − open PRs). That PR also adds the three countdown metrics you asked for (days-to-Hacktoberfest, issues/day, PRs/day).