Fixes [#24664] Improve System Message Formatting for Channel Header Edits (#24714)

* Added cancel button in the delete category modal

* fix lint error

* fix eslint issues

* Line break Added in system messages-ChannelHeader

* fix-lint

* Update _post.scss

* Update _markdown.scss

* Update system_message_helpers.tsx

* remove_extra_spaces

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Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/channels/src/components/post_markdown/system_message_helpers.tsx

@@ -189,7 +189,6 @@ function renderHeaderChangeMessage(post: Post): ReactNode {
     }
 
     const headerOptions = {
-        singleline: true,
         channelNamesMap: post.props && post.props.channel_mentions,
         mentionHighlight: true,
     };