DEP: Remove docutils upper-pin, bump Sphinx

This commit bumps the version of Sphinx
to 7 by relaxing the requirement on the version
of docutils. This allows building the docs with
a higher version of Sphinx on RTD and locally.

util/readthedocs/requirements.txt

@@ -1,5 +1,5 @@
 cython
-docutils<0.18
+docutils
 jupyterlite-sphinx>=0.14.0
 jupyterlite-pyodide-kernel
 pydata-sphinx-theme
@@ -8,6 +8,6 @@ matplotlib
 meson-python
 numpy
 numpydoc
-sphinx
+sphinx>=7
 sphinx-togglebutton
 sphinx-copybutton