build(deps): bump loguru from 0.7.2 to 0.7.3 in /backend

Bumps [loguru](https://github.com/Delgan/loguru) from 0.7.2 to 0.7.3.
- [Release notes](https://github.com/Delgan/loguru/releases)
- [Changelog](https://github.com/Delgan/loguru/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/Delgan/loguru/compare/0.7.2...0.7.3)

---
updated-dependencies:
- dependency-name: loguru
  dependency-version: 0.7.3
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

backend/requirements.txt

@@ -31,7 +31,7 @@ APScheduler==3.10.4
 
 RestrictedPython==8.0
 
-loguru==0.7.2
+loguru==0.7.3
 asgiref==3.8.1
 
 # AI libraries