Fix mypy checks failing in new types-docutils (#37858)

The types-docutils clarify type of some objects returned.

(cherry picked from commit 5f4bf90)

docs/exts/substitution_extensions.py

@@ -28,7 +28,7 @@
 from sphinx.transforms.post_transforms.code import HighlightLanguageTransform
 
 if TYPE_CHECKING:
-    from docutils.nodes import Node, system_message
+    from docutils.utils import SystemMessage
     from sphinx.application import Sphinx
 
 LOGGER = logging.getLogger(__name__)
@@ -86,7 +86,7 @@ def condition(node):
             node.rawsource = node.astext()
 
 
-def substitution_code_role(*args, **kwargs) -> tuple[list[Node], list[system_message]]:
+def substitution_code_role(*args, **kwargs) -> tuple[list, list[SystemMessage]]:
     """Decorate an inline code so that SubstitutionCodeBlockTransform will notice it"""
     [node], system_messages = code_role(*args, **kwargs)
     node[_SUBSTITUTION_OPTION_NAME] = True