Update sphinx requirements (#137)

* Update sphinx requirement from ==5.* to ==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/v8.1.3/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v5.0.0b1...v8.1.3)

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

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

* Update sphinx-autobuild requirement from ==2021.3.* to ==2024.10.*

Updates the requirements on [sphinx-autobuild](https://github.com/sphinx-doc/sphinx-autobuild) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx-autobuild/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx-autobuild/blob/main/NEWS.rst)
- [Commits](sphinx-doc/sphinx-autobuild@2021.03.14...2024.10.03)

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

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

* Update pydata-sphinx-theme requirement from ==0.15.* to ==0.16.*

Updates the requirements on [pydata-sphinx-theme](https://github.com/pydata/pydata-sphinx-theme) to permit the latest version.
- [Release notes](https://github.com/pydata/pydata-sphinx-theme/releases)
- [Changelog](https://github.com/pydata/pydata-sphinx-theme/blob/main/RELEASE.md)
- [Commits](pydata/pydata-sphinx-theme@v0.15.0rc0...v0.16.0)

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

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

---------

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

docs/requirements.txt

@@ -1,7 +1,7 @@
 livereload
-pydata-sphinx-theme==0.15.*
-sphinx==5.*
-sphinx-autobuild==2021.3.*
+pydata-sphinx-theme==0.16.*
+sphinx==8.*
+sphinx-autobuild==2024.10.*
 sphinx_rtd_theme
 sphinx-reredirects==0.1.*
 sphinxcontrib-redoc==1.6.0