Fix sphinx-doc#9718: intersphinx: Failed to invoke sphinx.ext.intersphinx module

A circular import was happened since sphinx-doc#9701 merged.  This goes
lazy-import to avoid the error.

Author: tk0miya

sphinx/addnodes.py

@@ -13,8 +13,6 @@
 from docutils import nodes
 from docutils.nodes import Element
 
-from sphinx.util import docutils
-
 if TYPE_CHECKING:
     from sphinx.application import Sphinx
 
@@ -530,6 +528,8 @@ class manpage(nodes.Inline, nodes.FixedTextElement):
 
 
 def setup(app: "Sphinx") -> Dict[str, Any]:
+    from sphinx.util import docutils  # lazy import
+
     app.add_node(toctree)
 
     app.add_node(desc)