Update sphinx requirement from ^4.0.2 to >=4.0.2,<7.0.0 (#179)

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@v4.0.2...v6.1.3)

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

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

pyproject.toml

@@ -37,7 +37,7 @@ flake8 = {version = "^5.0", optional = true}
 tox-gh-actions = {version = "^2.11", optional = true}
 doc8 = {version = "^0.11.0", optional = true}
 readme-renderer = {version = ">=35,<38", optional = true}
-Sphinx = {version = "^4.0.2", optional = true}
+Sphinx = {version = ">=4.0.2,<7.0.0", optional = true}
 sphinx-rtd-theme = {version = "^1.0.0", optional = true}
 sphinx-autodoc-typehints = {version = "^1.12.0", optional = true}
 sphinx-gallery = {version = ">=0.10,<0.12", optional = true}