Bump black from 23.3.0 to 24.3.0 in /backend

Bumps [black](https://github.com/psf/black) from 23.3.0 to 24.3.0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](psf/black@23.3.0...24.3.0)

---
updated-dependencies:
- dependency-name: black
  dependency-version: 24.3.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

backend/requirements-dev.txt

@@ -1,4 +1,4 @@
-black==23.3.0
+black==24.3.0
 isort==5.12.0
 flake8==6.0.0
 mypy==1.3.0