Bump rdf from 3.1.4 to 3.2.9

Bumps [rdf](https://github.com/ruby-rdf/rdf) from 3.1.4 to 3.2.9.
- [Release notes](https://github.com/ruby-rdf/rdf/releases)
- [Changelog](https://github.com/ruby-rdf/rdf/blob/develop/CHANGES.md)
- [Commits](https://github.com/ruby-rdf/rdf/compare/3.1.4...3.2.9

)

---
updated-dependencies:
- dependency-name: rdf
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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