deps(book): update attrs requirement from >=23.0.0 to >=26.1.0 (#1728)

Updates the requirements on [attrs](https://github.com/python-attrs/attrs) to permit the latest version.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/main/CHANGELOG.md)
- [Commits](python-attrs/attrs@23.1.0...26.1.0)

---
updated-dependencies:
- dependency-name: attrs
  dependency-version: 26.1.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

book/tools/dependencies/requirements.txt

@@ -53,7 +53,7 @@ seaborn>=0.13.2
 # the jupyter kernel crashes on startup with "Broken pipe (os error 32)".
 # Pinning it explicitly so a fresh `pip install -r requirements.txt`
 # produces a working build environment.
-attrs>=23.0.0
+attrs>=26.1.0
 
 # --- EPUB validation ---
 # Wraps the W3C `epubcheck` jar so `./binder check epub --scope epubcheck`