`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:
src/gui.c:48:13: error: format not a string literal and no format arguments [-Werror=format-security]
48 | card_suits[card->suit]);
| ^~~~~~~~~~
Let's wrap all the missing places with "%s" format.
