release-notes: update note with correct pr #
We are no longer relying on garden to clean up hijacked containers. Instead, we have implemented this functionality in concourse itself. This makes it much more portable to different container backends.
-##### <sub><sup><a name="5305" href="#5305">:link:</a></sup></sub> feature
+##### <sub><sup><a name="5431" href="#5431">:link:</a></sup></sub> feature
* We've updated the way that containers associated with failed runs get garbage collected
