relnotes: enable extension when running releasenotes command
Last night, when I was working on different machine, the test worked, now on a
different machine it does not. Looks like we should make sure releasenotes
extension is loaded.
Differential Revision: https://phab.mercurial-scm.org/D4425
{header}
<id>{urlbase}{url|urlescape}</id>
<link rel="self" href="{urlbase}{url|urlescape}atom-bookmarks"/>
<link rel="alternate" href="{urlbase}{url|urlescape}bookmarks"/>
<title>{repo|escape}: bookmarks</title>
<summary>{repo|escape} bookmark history</summary>
<author><name>Mercurial SCM</name></author>
{lastchange%feedupdated}
{entries%bookmarkentry}
</feed>