Bump async-trait from 0.1.63 to 0.1.68 in /backend

Bumps [async-trait](https://github.com/dtolnay/async-trait) from 0.1.63 to 0.1.68.
- [Release notes](https://github.com/dtolnay/async-trait/releases)
- [Commits](dtolnay/async-trait@0.1.63...0.1.68)

---
updated-dependencies:
- dependency-name: async-trait
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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