Fix a refcount.

Author: ericsnowcurrently

Modules/_interpretersmodule.c

@@ -271,6 +271,7 @@ _run_script(PyInterpreterState *interp, const char *codestr,
     if (main_mod == NULL)
         return -1;
     PyObject *ns = PyModule_GetDict(main_mod);  // borrowed
+    Py_INCREF(ns);
     Py_DECREF(main_mod);
     if (ns == NULL)
         return -1;