vim-patch:9.0.0206: redraw flags are not named specifically (#19913)

Problem:    Redraw flags are not named specifically.
Solution:   Prefix "UPD_" to the flags, for UPDate_screen().
a4d158b3c8

src/nvim/getchar.c

@@ -1750,7 +1750,7 @@ static void getchar_common(typval_T *argvars, typval_T *rettv)
 
   if (!ui_has_messages()) {
     // redraw the screen after getchar()
-    update_screen(CLEAR);
+    update_screen(UPD_CLEAR);
   }
 
   set_vim_var_nr(VV_MOUSE_WIN, 0);