gh-83004: Clean up refleak in _io initialisation (GH-98840)

(cherry picked from commit 1208037)

Co-authored-by: Shantanu <[email protected]>

Author: miss-islington

Misc/NEWS.d/next/Library/2022-11-02-05-52-36.gh-issue-83004.LBl79O.rst

@@ -0,0 +1 @@
+Clean up refleak on failed module initialisation in :mod:`_io`.

Modules/_io/_iomodule.c

@@ -718,10 +718,10 @@ PyInit__io(void)
         goto fail;
 
     /* BlockingIOError, for compatibility */
-    Py_INCREF(PyExc_BlockingIOError);
-    if (PyModule_AddObject(m, "BlockingIOError",
-                           (PyObject *) PyExc_BlockingIOError) < 0)
+    if (PyModule_AddObjectRef(m, "BlockingIOError",
+                              (PyObject *) PyExc_BlockingIOError) < 0) {
         goto fail;
+    }
 
     /* Concrete base types of the IO ABCs.
        (the ABCs themselves are declared through inheritance in io.py)