bpo-43844: Fix PendingDeprecationWarning in test_lib2to3 (GH-25407)

Author: vstinner

Lib/lib2to3/tests/test_parser.py

@@ -84,12 +84,16 @@ def test_load_grammar_from_subprocess(self):
             # different hash randomization seed.
             sub_env = dict(os.environ)
             sub_env['PYTHONHASHSEED'] = 'random'
-            subprocess.check_call(
-                    [sys.executable, '-c', """
+            code = """
 from lib2to3.pgen2 import driver as pgen2_driver
 pgen2_driver.load_grammar(%r, save=True, force=True)
-                    """ % (grammar_sub_copy,)],
-                    env=sub_env)
+            """ % (grammar_sub_copy,)
+            msg = ("lib2to3 package is deprecated and may not be able "
+                   "to parse Python 3.10+")
+            cmd = [sys.executable,
+                   f'-Wignore:{msg}:PendingDeprecationWarning',
+                   '-c', code]
+            subprocess.check_call( cmd, env=sub_env)
             self.assertTrue(os.path.exists(pickle_sub_name))
 
             with open(pickle_name, 'rb') as pickle_f_1, \