build(deps): bump black from 24.10.0 to 25.9.0 in /book/src

Bumps [black](https://github.com/psf/black) from 24.10.0 to 25.9.0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](psf/black@24.10.0...25.9.0)

---
updated-dependencies:
- dependency-name: black
  dependency-version: 25.9.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

book/src/requirements.txt

@@ -1,4 +1,4 @@
-black==24.10.0
+black==25.9.0
 coverage==7.10.6
 flake8==7.1.2
 hypothesis==6.139.2