bpo-42246: Partial implementation of PEP 626. (GH-23113)

* Implement new line number table format, as defined in PEP 626.
diff --git a/Lib/test/test_pdb.py b/Lib/test/test_pdb.py
index e564513..4bb574f 100644
--- a/Lib/test/test_pdb.py
+++ b/Lib/test/test_pdb.py
@@ -1645,9 +1645,10 @@ def test_errors_in_command(self):
             'debug doesnotexist',
             'c',
         ])
-        stdout, _ = self.run_pdb_script('', commands + '\n')
+        stdout, _ = self.run_pdb_script('pass', commands + '\n')
 
         self.assertEqual(stdout.splitlines()[1:], [
+            '-> pass',
             '(Pdb) *** SyntaxError: unexpected EOF while parsing',
 
             '(Pdb) ENTERING RECURSIVE DEBUGGER',