Update sphinx requirement from <7,>=3.5 to >=3.5,<8

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.5.0...v7.0.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
...

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

Author: dependabot[bot]

setup.py

@@ -76,7 +76,7 @@ def read(path):
               # `test_http.py` needs `setuptools.ssl_support`
               'setuptools<57',
               ],
-        doc=['sphinx>=3.5,<7',
+        doc=['sphinx>=3.5,<8',
              'crate-docs-theme>=0.26.5'],
     ),
     python_requires='>=3.6',