Bump flake8 from 6.1.0 to 7.1.1 in /book/src

Bumps [flake8](https://github.com/pycqa/flake8) from 6.1.0 to 7.1.1.
- [Commits](PyCQA/flake8@6.1.0...7.1.1)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

book/src/requirements.txt

@@ -1,6 +1,6 @@
 black==24.8.0
 coverage==7.6.1
-flake8==6.1.0
+flake8==7.1.1
 hypothesis==6.112.0
 isort==5.13.2
 MutPy==0.6.1