requirements: update sphinx-autodoc-typehints requirement

Updates the requirements on [sphinx-autodoc-typehints](https://github.com/tox-dev/sphinx-autodoc-typehints) to permit the latest version.
- [Release notes](https://github.com/tox-dev/sphinx-autodoc-typehints/releases)
- [Changelog](https://github.com/tox-dev/sphinx-autodoc-typehints/blob/main/CHANGELOG.md)
- [Commits](tox-dev/sphinx-autodoc-typehints@1.0.0...2.5.0)

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

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

doc_requirements.txt

@@ -1,3 +1,3 @@
 psyneulink-sphinx-theme<1.2.4.1
 sphinx<4.2.1
-sphinx_autodoc_typehints<1.16.0
+sphinx_autodoc_typehints<2.6.0