Update sphinx requirement from ~=4.2.0 to ~=7.2.6 (#94)

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@v4.2.0...v7.2.6)

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

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

requirements_dev.txt

@@ -4,6 +4,6 @@ invoke
 coverage
 coveralls~=3.3.1
 rope~=1.7.0
-Sphinx~=4.2.0
+Sphinx~=7.2.6
 hfilesize~=0.1.0
 humanize~=4.4