changed string for ai_chai sidebar bootton's tooltip

Signed-off-by: Vadym Struts <vstruts@brave.com>

components/resources/ai_chat_ui_strings.grdp

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <grit-part>
   <message name="IDS_CHAT_UI_TITLE" translateable="false" desc="Title for the Brave AI product">
-    Brave AI
+    Brave Leo
   </message>
   <message name="IDS_CHAT_UI_SUMMARIZE_FAILED_LABEL" desc="Label for when summarization is not possible">
     The summarizer feature is currently available only for select articles and other long-form web pages.