chore(contrib): PKGBUILD version permanently stale — include in bump_version.py

[Kohei-Wada]

Problem

contrib/aur/PKGBUILD:4 is permanently stale: pkgver=0.22.0 while the repo is at 0.26.0, with a stale sha256sums. scripts/bump_version.py (discover_pyproject_files, verify_no_old_versions) only touches pyproject.toml files; the PKGBUILD is patched ad hoc by release.yml:160-163 at publish time, so the committed file never matches and a local makepkg from the repo fails.

Direction

Have bump_version.py rewrite pkgver (and set sha256sums to SKIP or regenerate) and include the PKGBUILD in verify_no_old_versions.

Found during repo-wide audit, 2026-07-25.