ci: run Test262 results updates manually

[pathscale]

The Test262 results workflow ran on every master push and published release, spending up to 60 minutes before failing in this fork because its external boa-dev/data write credential is unavailable.

Make the workflow manual-only, label that behavior in the Actions UI, and document that operators must configure DATA_PAT with external write access. The existing credential use for checkout and push remains unchanged.

Validation:

• Parsed .github/workflows/test262_release.yml with Ruby YAML
• git diff --check
• Confirmed the diff contains only the workflow file and no lockfiles
• cargo fmt -- --check passed through the push hook
• cargo clippy --all-features --all-targets is blocked by existing Rust 1.97 manual_assert_eq lints in unchanged source files