Bump defmt-rtt in /examples/stm32f4-single-motor-example

Bumps [defmt-rtt](https://github.com/knurling-rs/defmt) from 0.4.1 to 0.4.2.
- [Release notes](https://github.com/knurling-rs/defmt/releases)
- [Changelog](https://github.com/knurling-rs/defmt/blob/main/CHANGELOG.md)
- [Commits](https://github.com/knurling-rs/defmt/commits)

---
updated-dependencies:
- dependency-name: defmt-rtt
  dependency-version: 0.4.2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]