build(deps): bump yapf from 0.40.2 to 0.43.0 in /book/src

Bumps [yapf](https://github.com/google/yapf) from 0.40.2 to 0.43.0.
- [Changelog](https://github.com/google/yapf/blob/main/CHANGELOG.md)
- [Commits](google/yapf@v0.40.2...v0.43.0)

---
updated-dependencies:
- dependency-name: yapf
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

book/src/requirements.txt

@@ -14,4 +14,4 @@ pytest==8.3.3
 pytest-cov==5.0.0
 pytype==2024.9.13
 requests==2.32.3
-yapf==0.40.2
+yapf==0.43.0