build(deps-dev): bump @polkadot/typegen from 12.1.1 to 12.2.1

Bumps [@polkadot/typegen](https://github.com/polkadot-js/api/tree/HEAD/packages/typegen) from 12.1.1 to 12.2.1.
- [Release notes](https://github.com/polkadot-js/api/releases)
- [Changelog](https://github.com/polkadot-js/api/blob/master/CHANGELOG.md)
- [Commits](https://github.com/polkadot-js/api/commits/v12.2.1/packages/typegen)

---
updated-dependencies:
- dependency-name: "@polkadot/typegen"
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>