build(deps): bump gunicorn from 23.0.0 to 25.0.3 in /backend

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 23.0.0 to 25.0.3.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@23.0.0...25.0.3)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-version: 25.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -4,7 +4,7 @@ django-environ==0.12.0
 djangorestframework==3.16.1
 dockerflow==2024.4.2
 drf-yasg==1.21.11
-gunicorn==23.0.0
+gunicorn==25.0.3
 parsepatch==0.1.3
 psycopg2-binary==2.9.11
 sentry-sdk==2.52.0