Update sphinx requirement from <5.0,>=4.0 to >=4.0,<8.0 (#81)

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@v4.0.0...v7.0.1)

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

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

setup.py

@@ -31,7 +31,7 @@
             "Django",
             "psycopg2",
             "sphinx_rtd_theme>=1.0,<2.0",
-            "Sphinx>=4.0,<5.0",
+            "Sphinx>=4.0,<8.0",
         ],
         "test": [
             "coverage[toml]>=5,<6",