closes bpo-39859: Do not downcast result of hstrerror (GH-18790)

set_herror builds a string by calling hstrerror but downcasts its return value to char *.  It should be const char *.

Automerge-Triggered-By: @benjaminp

Modules/socketmodule.c

@@ -658,7 +658,7 @@ set_herror(int h_error)
     PyObject *v;
 
 #ifdef HAVE_HSTRERROR
-    v = Py_BuildValue("(is)", h_error, (char *)hstrerror(h_error));
+    v = Py_BuildValue("(is)", h_error, hstrerror(h_error));
 #else
     v = Py_BuildValue("(is)", h_error, "host not found");
 #endif