Backported setting of transcation.on=1 in THD::reset_for_reuse()

This is to ensure code in 10.4 and 10.5 is logically identical for this
variable

sql/sql_class.cc

@@ -1640,6 +1640,7 @@ void THD::reset_for_reuse()
   abort_on_warning= 0;
   free_connection_done= 0;
   m_command= COM_CONNECT;
+  transaction.on= 1;
 #if defined(ENABLED_PROFILING)
   profiling.reset();
 #endif