Bump tokio from 1.24.1 to 1.26.0 in /backend

Bumps [tokio](https://github.com/tokio-rs/tokio) from 1.24.1 to 1.26.0.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-1.24.1...tokio-1.26.0)

---
updated-dependencies:
- dependency-name: tokio
  dependency-type: indirect
...

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Author: dependabot[bot]