fix(chatform): remove std::dynamic_pointer_cast in favor of static cast

With the removal of RTTI such a cast can cause compile failures as not
all compilers automatically convert dynamic casts to static casts at
compile time.

Fixes #3801

src/widget/form/genericchatform.cpp

@@ -486,7 +486,7 @@ QString GenericChatForm::resolveToxId(const ToxId &id)
 
 void GenericChatForm::insertChatMessage(ChatMessage::Ptr msg)
 {
-    chatWidget->insertChatlineAtBottom(std::dynamic_pointer_cast<ChatLine>(msg));
+    chatWidget->insertChatlineAtBottom(std::static_pointer_cast<ChatLine>(msg));
     emit messageInserted();
 }