Bump flask-cors from 5.0.1 to 6.0.0 in /backend

Bumps [flask-cors](https://github.com/corydolphin/flask-cors) from 5.0.1 to 6.0.0.
- [Release notes](https://github.com/corydolphin/flask-cors/releases)
- [Changelog](https://github.com/corydolphin/flask-cors/blob/main/CHANGELOG.md)
- [Commits](corydolphin/flask-cors@5.0.1...6.0.0)

---
updated-dependencies:
- dependency-name: flask-cors
  dependency-version: 6.0.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -1,6 +1,6 @@
 Flask==3.1.0
 gunicorn==23.0.0
-flask-cors==5.0.1
+flask-cors==6.0.0
 gpxpy==1.6.2
 numpy==2.2.4
 geopy==2.4.1