Update sphinx requirement from ~=6.2.1 to ~=7.3.7 in /fdmlpy

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.rst)
- [Commits](sphinx-doc/sphinx@v6.2.1...v7.3.7)

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

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

fdmlpy/requirements.txt

@@ -1,3 +1,3 @@
 build~=0.10.0
-sphinx~=6.2.1
+sphinx~=7.3.7
 sphinx_rtd_theme~=1.2.0