chore(deps): bump mongodb from 3.5.0 to 3.5.1 in /reference-apps/rust

Bumps [mongodb](https://github.com/mongodb/mongo-rust-driver) from 3.5.0 to 3.5.1.
- [Release notes](https://github.com/mongodb/mongo-rust-driver/releases)
- [Commits](mongodb/mongo-rust-driver@v3.5.0...v3.5.1)

---
updated-dependencies:
- dependency-name: mongodb
  dependency-version: 3.5.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]