Bump sphinx from 4.4.0 to 8.1.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 4.4.0 to 8.1.3.
- [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@v4.4.0...v8.1.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

requirements.txt

@@ -4,7 +4,7 @@ matplotlib
 numpy
 pandas
 ghp-import
-#Sphinx==5.0.2 ## had been 4.4.0
+#Sphinx==8.1.3 ## had been 4.4.0
 sphinx-book-theme==0.1.10
 sphinx-comments==0.0.3
 sphinx-copybutton==0.5.0
@@ -21,6 +21,6 @@ sphinxcontrib-htmlhelp==2.0.0
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.3
 sphinxcontrib-serializinghtml==1.1.5
-Sphinx==5.0.2
+Sphinx==8.1.3
 sphinx-exercise==0.4.0
 sphinx-proof