build(deps): bump ethnum from 1.1.1 to 1.2.1

Bumps [ethnum](https://github.com/nlordell/ethnum-rs) from 1.1.1 to 1.2.1.
- [Release notes](https://github.com/nlordell/ethnum-rs/releases)
- [Commits](nlordell/ethnum-rs@v1.1.1...v1.2.1)

---
updated-dependencies:
- dependency-name: ethnum
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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