Add subset of ported static tests to `json_loader` CI

## Add ported static tests to `json_loader` CI

Follow-up to #2455.

The 2,180 ported static tests under `tests/ported_static/` are currently excluded from all CI jobs via `--ignore=tests/ported_static` in `tox.ini` (`py3`, `pypy3`, and `json_loader`).

We should integrate them into the `json_loader` job, which fills a minimized test subset and enforces a coverage gate (> 85%). This avoids adding them to `py3`/`pypy3` where they'd increase runtimes across the board. We could consider increasing this %.

### Proposed approach

1. Remove the `--ignore=tests/ported_static` from the `json_loader` tox env
2. Run `minimize-tests` against the combined set (existing `json_loader` tests + `ported_static`) to find a new minimal subset that maintains the coverage threshold
3. Add `@pytest.mark.json_loader` to the selected ported tests (minimal)
4. Verify `json_loader` CI runtime remains reasonable