build(deps): bump serial_test from 3.2.0 to 3.3.1

Bumps [serial_test](https://github.com/palfrey/serial_test) from 3.2.0 to 3.3.1.
- [Release notes](https://github.com/palfrey/serial_test/releases)
- [Commits](palfrey/serial_test@v3.2.0...v3.3.1)

---
updated-dependencies:
- dependency-name: serial_test
  dependency-version: 3.3.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]