use the new DoLogString signature (fixes with 2.8 compat switched off)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53393 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/keyboard/keyboard.cpp

@@ -116,7 +116,7 @@ private:
         }
     }
 
-    virtual void DoLogString(const wxChar *szString, time_t WXUNUSED(t))
+    virtual void DoLogString(const wxString& szString, time_t WXUNUSED(t))
     {
         wxString msg;
         TimeStamp(&msg);