Fix highlight mentions not updating when username changes (#6723)

Reported-by: James Upjohn <jupjohn@jammeh.co.nz>
Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>
Reviewed-by: Nerixyz <nerixdev@outlook.de>

src/providers/twitch/TwitchAccountManager.hpp

@@ -70,6 +70,7 @@ public:
 
     boost::signals2::signal<void()> currentUserChanged;
     pajlada::Signals::NoArgSignal userListUpdated;
+    pajlada::Signals::NoArgSignal currentUserNameChanged;
 
     SignalVector<std::shared_ptr<TwitchAccount>> accounts;