Update qiskit-sphinx-theme requirement from ~=1.16.0 to ~=2.0.0

Updates the requirements on [qiskit-sphinx-theme](https://github.com/Qiskit/qiskit_sphinx_theme) to permit the latest version.
- [Release notes](https://github.com/Qiskit/qiskit_sphinx_theme/releases)
- [Changelog](https://github.com/Qiskit/qiskit_sphinx_theme/blob/main/docs_guide/release_notes.rst)
- [Commits](Qiskit/qiskit_sphinx_theme@1.16.0...2.0.0)

---
updated-dependencies:
- dependency-name: qiskit-sphinx-theme
  dependency-version: 2.0.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -9,7 +9,7 @@ mypy-extensions>=0.4.4
 jupyter-sphinx>=0.5.3
 nbsphinx>=0.9.7
 sphinx-autodoc-typehints>=1.24.0
-qiskit-sphinx-theme~=1.16.0
+qiskit-sphinx-theme~=2.0.0
 reno>=3.5.0
 # Black's formatting rules can change between major versions, so we use
 # the ~= specifier for it.