build(deps): bump pyflakes from 3.2.0 to 3.4.0 in /book/src

Bumps [pyflakes](https://github.com/PyCQA/pyflakes) from 3.2.0 to 3.4.0.
- [Changelog](https://github.com/PyCQA/pyflakes/blob/main/NEWS.rst)
- [Commits](PyCQA/pyflakes@3.2.0...3.4.0)

---
updated-dependencies:
- dependency-name: pyflakes
  dependency-version: 3.4.0
  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

@@ -8,7 +8,7 @@ mypy==1.16.1
 mypy-extensions==1.1.0
 pinject==0.14.1
 pip-tools==7.4.1
-pyflakes==3.2.0
+pyflakes==3.4.0
 pylint==3.3.7
 pytest==8.4.1
 pytest-cov==5.0.0