Bump flask in /backend in the pip group across 1 directory

Bumps the pip group with 1 update in the /backend directory: [flask](https://github.com/pallets/flask).


Updates `flask` from 2.3.2 to 3.1.3
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](pallets/flask@2.3.2...3.1.3)

---
updated-dependencies:
- dependency-name: flask
  dependency-version: 3.1.3
  dependency-type: direct:production
  dependency-group: pip
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/requirements.txt

@@ -4,7 +4,7 @@ numpy_stl==3.0.1
 pyaudio
 opencv-contrib-python
 matplotlib==3.7.1
-flask==2.3.2
+flask==3.1.3
 flask_cors==4.0.0
 scipy~=1.10.1
 plotly_express