bpo-34491: Add missing Py_DECREF() in _bsddb's DB_join() (GH-8909)

diff --git a/Modules/_bsddb.c b/Modules/_bsddb.c
index 6a1c188..cee447b 100644
--- a/Modules/_bsddb.c
+++ b/Modules/_bsddb.c
@@ -2297,6 +2297,7 @@
             PyErr_SetString(PyExc_TypeError,
                             "Sequence of DBCursor objects expected");
             free(cursors);
+            Py_DECREF(item);
             return NULL;
         }
         cursors[x] = ((DBCursorObject*)item)->dbc;