build(deps): bump ffi from 1.15.4 to 1.15.5 in /docs

Bumps [ffi](https://github.com/ffi/ffi) from 1.15.4 to 1.15.5.
- [Release notes](https://github.com/ffi/ffi/releases)
- [Changelog](https://github.com/ffi/ffi/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ffi/ffi/compare/v1.15.4...v1.15.5)

---
updated-dependencies:
- dependency-name: ffi
  dependency-type: indirect
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>