pip(deps-dev): update black requirement in /backend

Updates the requirements on [black](https://github.com/psf/black) to permit the latest version.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](psf/black@23.1a1...24.10.0)

---
updated-dependencies:
- dependency-name: black
  dependency-type: direct:development
...

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

Author: dependabot[bot]

backend/requirements-dev.txt

@@ -1,5 +1,5 @@
 # Development dependencies
-black==23.*
+black==24.*
 isort==5.*
 flake8==6.*
 pytest==7.*