Update sphinx requirement from <8.0 to <9.0 (#2235)

* Update sphinx requirement from <8.0 to <9.0

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/v8.0.2/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v0.1.61611...v8.0.2)

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

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

* Update requirements.txt

* Update pyproject.toml

* Update pyproject.toml

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Samet Akcay <samet.akcay@intel.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,7 +1,7 @@
 myst-parser
 nbsphinx
 pandoc
-sphinx<8.0  # 7.0 breaks readthedocs builds.
+sphinx
 sphinx_autodoc_typehints
 sphinx_book_theme
 sphinx-copybutton

pyproject.toml

@@ -68,7 +68,7 @@ docs = [
     "myst-parser",
     "nbsphinx",
     "pandoc",
-    "sphinx<8.0",  # 7.0 breaks readthedocs builds.
+    "sphinx",
     "sphinx_autodoc_typehints",
     "sphinx_book_theme",
     "sphinx-copybutton",