Drop old Sphinx version constraint to pick up global constraint

x-ref
inducer/ci-support@112ab59

Author: inducer

.github/workflows/ci.yml

@@ -106,8 +106,6 @@ jobs:
                 curl -L -O https://tiker.net/ci-support-v0
                 . ./ci-support-v0
                 build_py_project_in_venv
-                # https://github.com/sphinx-doc/sphinx/issues/9200
-                CI_SUPPORT_SPHINX_VERSION_SPECIFIER="!=4.0.0"
                 build_docs
 
     downstream_tests: