fix refcount error

Author: smola

ddtrace/appsec/_iast/_stacktrace.c

@@ -252,7 +252,7 @@ _get_result_tuple(PyFrameObject* frame)
     result = PyTuple_Pack(4, filename_o, line_o, funcname_o, classname_o);
 
 error:
-    Py_XDECREF(filename_o);
+    FILENAME_XDECREF(filename_o);
     Py_XDECREF(line_o);
     Py_XDECREF(funcname_o);
     Py_XDECREF(classname_o);