fix: User Mentioning when prepending the username with > (#28875)

Co-authored-by: Hugo Costa <hugocarreiracosta@gmail.com>
Co-authored-by: Guilherme Gazzo <guilhermegazzo@gmail.com>

.changeset/user-mention.md

+---
+"@rocket.chat/meteor": patch
+---
+
+Fixed user mentioning when prepending the username with `>`

apps/meteor/app/mentions/lib/MentionsParser.js

@@ -38,7 +38,7 @@ export class MentionsParser {
 	}
 
 	get userMentionRegex() {
-		return new RegExp(`(^|\\s|> ?)@(${this.pattern}(@(${this.pattern}))?(:([0-9a-zA-Z-_.]+))?)`, 'gm');
+		return new RegExp(`(^|\\s|>)@(${this.pattern}(@(${this.pattern}))?(:([0-9a-zA-Z-_.]+))?)`, 'gm');
 	}
 
 	get channelMentionRegex() {