Bump sphinx from 7.1.2 to 7.2.6 in /third_party/airflow

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.1.2 to 7.2.6.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.1.2...v7.2.6)

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

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

third_party/airflow/pyproject.toml

@@ -22,7 +22,7 @@ readme = "README.md"
 format = ["black==23.7.0", "flake8==6.1.0", "pylint==2.17.5"]
 test = ["pytest==7.3.1", "coverage==7.3.1", "pytest-asyncio==0.21.1"]
 # note(JayF): sphinx-jekyll-builder was broken by sphinx-markdown-builder 0.6 -- so pin to 0.5.5
-docs = ["sphinx==7.1.2", "sphinx-jekyll-builder==0.3.0", "sphinx-toolbox==3.2.0b1", "sphinx-markdown-builder==0.5.5"]
+docs = ["sphinx==7.2.6", "sphinx-jekyll-builder==0.3.0", "sphinx-toolbox==3.2.0b1", "sphinx-markdown-builder==0.5.5"]
 
 [build-system]
 requires = ["setuptools"]