bpo-36430: Fix a possible reference leak in itertools.count(). (GH-12551)

(cherry picked from commit 0523c39e7720b82b38ad793d3f1a5681adcdf873)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 1113fb6..bff9df6 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -4027,6 +4027,7 @@
     lz = (countobject *)type->tp_alloc(type, 0);
     if (lz == NULL) {
         Py_XDECREF(long_cnt);
+        Py_DECREF(long_step);
         return NULL;
     }
     lz->cnt = cnt;