Update sphinx-rtd-theme requirement (#40)

Updates the requirements on [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) to permit the latest version.
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@2.0.0...3.0.1)

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

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

pyproject.toml

@@ -41,7 +41,7 @@ dependencies = ["numpy", "openqasm3[parser]>=1.0.0,<2.0.0"]
 [project.optional-dependencies]
 test = ["pytest", "pytest-cov"]
 lint = ["black", "isort", "pylint", "mypy", "qbraid-cli>=0.8.5"]
-docs = ["sphinx>=7.3.7,<8.1.0", "sphinx-autodoc-typehints>=1.24,<2.5", "sphinx-rtd-theme>=2.0.0,<3.0.0", "docutils<0.22", "sphinx-copybutton"]
+docs = ["sphinx>=7.3.7,<8.1.0", "sphinx-autodoc-typehints>=1.24,<2.5", "sphinx-rtd-theme>=2.0.0,<4.0.0", "docutils<0.22", "sphinx-copybutton"]
 
 [tool.setuptools_scm]
 write_to = "pyqasm/_version.py"