bpo-34967: Sphinx is deprecating add_description_unit, use add_object_type (GH-9827)

diff --git a/Doc/tools/extensions/pyspecific.py b/Doc/tools/extensions/pyspecific.py
index 132920f..08fa9df 100644
--- a/Doc/tools/extensions/pyspecific.py
+++ b/Doc/tools/extensions/pyspecific.py
@@ -424,11 +424,9 @@
     app.add_directive('deprecated-removed', DeprecatedRemoved)
     app.add_builder(PydocTopicsBuilder)
     app.add_builder(suspicious.CheckSuspiciousMarkupBuilder)
-    app.add_description_unit('opcode', 'opcode', '%s (opcode)',
-                             parse_opcode_signature)
-    app.add_description_unit('pdbcommand', 'pdbcmd', '%s (pdb command)',
-                             parse_pdb_command)
-    app.add_description_unit('2to3fixer', '2to3fixer', '%s (2to3 fixer)')
+    app.add_object_type('opcode', 'opcode', '%s (opcode)', parse_opcode_signature)
+    app.add_object_type('pdbcommand', 'pdbcmd', '%s (pdb command)', parse_pdb_command)
+    app.add_object_type('2to3fixer', '2to3fixer', '%s (2to3 fixer)')
     app.add_directive_to_domain('py', 'decorator', PyDecoratorFunction)
     app.add_directive_to_domain('py', 'decoratormethod', PyDecoratorMethod)
     app.add_directive_to_domain('py', 'coroutinefunction', PyCoroutineFunction)