Bump flask from 1.1.2 to 2.2.5 in /backend (#42)

Bumps [flask](/~https://github.com/pallets/flask) from 1.1.2 to 2.2.5.
- [Release notes](/~https://github.com/pallets/flask/releases)
- [Changelog](/~https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](pallets/flask@1.1.2...2.2.5)

---
updated-dependencies:
- dependency-name: flask
  dependency-type: direct:production
...

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