Ui.cpp: always use "%s"-style format for printf()-style functions

[trofi]

ncuses-6.3 added printf-style function attributes and now makes it easier to catch cases when user input is used in palce of format string when built with CFLAGS=-Werror=format-security:

Ui.cpp:293:16: error: format not a string literal and no format arguments [-Werror=format-security]
  293 |       mvwprintw(w,0,0,msg.c_str());
      |       ~~~~~~~~~^~~~~~~~~~~~~~~~~~~

Let's wrap all the missing places with "%s" format.