bpo-22273: Re-enabled ctypes test on ARM machines. (GH-16388)

diff --git a/Lib/ctypes/test/test_structures.py b/Lib/ctypes/test/test_structures.py
index 661efc1..fedcae2 100644
--- a/Lib/ctypes/test/test_structures.py
+++ b/Lib/ctypes/test/test_structures.py
@@ -480,7 +480,7 @@
         self.assertEqual(s.first, got.first)
         self.assertEqual(s.second, got.second)
 
-    @unittest.skipIf(MACHINE.startswith(('arm', 'ppc')),
+    @unittest.skipIf(MACHINE.startswith('ppc'),
                      'Test temporarily disabled on this architecture')
     def test_array_in_struct(self):
         # See bpo-22273