[3.14] Add classmethod to setUpClass in test_pdb (pythonGH-133840) (python#133846)

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

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

Author: miss-islington

Lib/test/test_pdb.py

@@ -4749,7 +4749,9 @@ def test_return_from_inline_mode_to_REPL(self):
 @support.force_not_colorized_test_class
 @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')