When `$type` is `atom` in `get_the_category_rss()`, use `get_bloginfo_rss( 'url' )` when setting the `scheme` attribute for the `<category>` node.

Props ejdanderson.
Fixes #24444.



git-svn-id: https://develop.svn.wordpress.org/trunk@28258 602fd350-edb4-49c9-b593-d223f7449a82