DOC: Use the old class-based autodoc with Sphinx 9

The new version appears to be causing some issues for our missing
reference checks, so reverting back to the old implementation should buy
us some time to fix things.

Author: QuLogic

doc/conf.py

@@ -899,3 +899,4 @@ def setup(app):
     if sphinx.version_info[:2] < (7, 1):
         app.connect('html-page-context', add_html_cache_busting, priority=1000)
     generate_ScalarMappable_docs()
+    app.config.autodoc_use_legacy_class_based = True

lib/matplotlib/backend_tools.pyi

@@ -112,10 +112,10 @@ class ToolHelpBase(ToolBase):
 
 class ToolCopyToClipboardBase(ToolBase): ...
 
-default_tools: dict[str, ToolBase]
+default_tools: dict[str, type[ToolBase]]
 default_toolbar_tools: list[list[str | list[str]]]
 
 def add_tools_to_manager(
-    toolmanager: ToolManager, tools: dict[str, type[ToolBase]] = ...
+    toolmanager: ToolManager, tools: dict[str, type[ToolBase]] | None = ...
 ) -> None: ...
-def add_tools_to_container(container: ToolContainerBase, tools: list[Any] = ...) -> None: ...
+def add_tools_to_container(container: ToolContainerBase, tools: list[Any] | None = ...) -> None: ...