Issue #26637: Fix test_io

The import machinery now raises a different exception when it fails at Python
shutdown.
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 86440c5..37b9b2d 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -3079,8 +3079,7 @@
 
 class PyTextIOWrapperTest(TextIOWrapperTest):
     io = pyio
-    #shutdown_error = "LookupError: unknown encoding: ascii"
-    shutdown_error = "TypeError: 'NoneType' object is not iterable"
+    shutdown_error = "LookupError: unknown encoding: ascii"
 
 
 class IncrementalNewlineDecoderTest(unittest.TestCase):