bpo-39831: Remove outdated comment. (GH-18764)

diff --git a/Python/_warnings.c b/Python/_warnings.c
index 92378fa..39f8033 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -889,11 +889,9 @@
     return 1;
 
  handle_error:
-    /* filename not XDECREF'ed here as there is no way to jump here with a
-       dangling reference. */
     Py_XDECREF(*registry);
     Py_XDECREF(*module);
-    Py_XDECREF(*filename);
+    Py_DECREF(*filename);
     return 0;
 }