Bump flask from 1.1.2 to 2.2.5 in /backend

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
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -3,7 +3,7 @@ luigi==2.8.11
 plotnine==0.7.0
 #rpy2==3.3.5
 celery==5.1.2
-flask==1.1.2
+flask==2.2.5
 flask-cors
 flask-socketio==4.3.1
 python-socketio>=4.3.0,<5