build(deps): bump mypy from 1.12.0 to 1.12.1 in /book/src

Bumps [mypy](https://github.com/python/mypy) from 1.12.0 to 1.12.1.
- [Changelog](https://github.com/python/mypy/blob/master/CHANGELOG.md)
- [Commits](python/mypy@v1.12.0...v1.12.1)

---
updated-dependencies:
- dependency-name: mypy
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

book/src/requirements.txt

@@ -4,7 +4,7 @@ flake8==7.1.1
 hypothesis==6.115.3
 isort==5.13.2
 MutPy==0.6.1
-mypy==1.12.0
+mypy==1.12.1
 mypy-extensions==1.0.0
 pinject==0.14.1
 pip-tools==7.4.1