Change order of io.UnsupportedOperation base classes.
This makes tests passing after changes by issue #5322.
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 0d98b74..f2fe447 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -276,7 +276,7 @@
 try:
     UnsupportedOperation = io.UnsupportedOperation
 except AttributeError:
-    class UnsupportedOperation(ValueError, OSError):
+    class UnsupportedOperation(OSError, ValueError):
         pass