⬆️ Update furo requirement

Updates the requirements on [furo](https://github.com/pradyunsg/furo) to permit the latest version.
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](pradyunsg/furo@2022.06.04...2023.05.20)

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

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

pyproject.toml

@@ -43,7 +43,7 @@ testing = [
     "pytest-cov",
     "pytest-regressions",
 ]
-theme_furo = ["furo>=2022.06.04,<2022.07"]
+theme_furo = ["furo>=2022.06.04,<2023.6"]
 theme_pydata = ["pydata-sphinx-theme~=0.9.0"]
 theme_rtd = ["sphinx-rtd-theme~=1.0"]
 theme_sbt = ["sphinx-book-theme~=0.3.0"]