Fix pr-status job pagination (#94049)
### What?
Lower the GitHub Actions jobs page size used by `scripts/pr-status.js`
and keep walking pages until all jobs are fetched. Reuse the paginated
job fetch for flaky-test detection.
### Why?
The previous `per_page=100&page=1` request for run `26093602659` returns
HTTP 502 from GitHub because the query is too slow.
### How?
Add a shared `JOBS_PAGE_SIZE = 30`, update the pagination stop condition
to match it, and route flaky-test failed job lookup through
`getFailedJobs()`.
### Verification
- `node --check scripts/pr-status.js`
- `pnpm prettier --with-node-modules --ignore-path .prettierignore
--write scripts/pr-status.js`
- `npx eslint --config eslint.config.mjs --fix scripts/pr-status.js`
- `gh api
"repos/vercel/next.js/actions/runs/26093602659/jobs?per_page=30&page=<n>"
--jq ".jobs | length"` across pages 1-5 captured 137 jobs, matching
`total_count: 137`
- Confirmed the old `per_page=100&page=1` request still returns HTTP 502
- Not run: full Next.js test suite (scripts-only helper change)
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