add release note
concourse/concourse#4346
#### <sub><sup><a name="v550-note-29" href="#v550-note-29">:link:</a></sup></sub> fix
* Scrollbars have been given a touch of the Concourse design language. It should no longer use browser defaults. #4355
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+#### <sub><sup><a name="v550-note-4375" href="#v550-note-4375">:link:</a></sup></sub> fix
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+* Fixed a (probably-long-standing) issue where the pipelines in the sidebar could [randomly rearrange](https://github.com/concourse/concourse/issues/4346) #4375.
