Issue #25622: Use repr(bytes) to avoid BytesWarning

Author: vadmium

Lib/ctypes/test/test_values.py

@@ -75,7 +75,7 @@ class struct_frozen(Structure):
             if entry.name in bootstrap_expected:
                 bootstrap_seen.append(entry.name)
                 self.assertTrue(entry.size,
-                    "{} was reported as having no size".format(entry.name))
+                    "{!r} was reported as having no size".format(entry.name))
                 continue
             items.append((entry.name, entry.size))