bpo-36350: inspect: Replace OrderedDict with dict. (GH-12412)

diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index d95e742..8a2efc8 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -2077,6 +2077,7 @@
         P = inspect.Parameter
 
         self.assertEqual(str(S()), '()')
+        self.assertEqual(repr(S().parameters), 'mappingproxy({})')
 
         def test(po, pk, pod=42, pkd=100, *args, ko, **kwargs):
             pass
@@ -3681,6 +3682,10 @@
         ba.apply_defaults()
         self.assertEqual(list(ba.arguments.items()), [('a', 'spam')])
 
+    def test_signature_bound_arguments_arguments_type(self):
+        def foo(a): pass
+        ba = inspect.signature(foo).bind(1)
+        self.assertIs(type(ba.arguments), dict)
 
 class TestSignaturePrivateHelpers(unittest.TestCase):
     def test_signature_get_bound_param(self):