[3.13] Add classmethod to setUpClass in test_pdb (GH-133840) (#133847)

Add classmethod to setUpClass in test_pdb (GH-133840)
(cherry picked from commit 4f2f780)

Co-authored-by: Tian Gao <gaogaotiantian@hotmail.com>

Author: miss-islington

Lib/test/test_pdb.py

@@ -4022,7 +4022,9 @@ def test_checkline_is_not_executable(self):
 
 @support.requires_subprocess()
 class PdbTestReadline(unittest.TestCase):
-    def setUpClass():
+
+    @classmethod
+    def setUpClass(cls):
         # Ensure that the readline module is loaded
         # If this fails, the test is skipped because SkipTest will be raised
         readline = import_module('readline')