ncurses: avoid warnings about too-long initializer strings

[dim]

Summary

Increase the size of assoc::from to 8 bytes, to avoid warnings from
clang 21 similar to:

contrib/ncurses/progs/infocmp.c:702:10: error: initializer-string for character array is too long, array size is 4 but initializer has size 5 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Werror,-Wunterminated-string-initialization]
  702 |     DATA("\033[2J", "ED2"),     /* clear page */
      |          ^~~~~~~~~
contrib/ncurses/progs/infocmp.c:716:10: error: initializer-string for character array is too long, array size is 4 but initializer has size 5 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Werror,-Wunterminated-string-initialization]
  716 |     DATA("\033[!p", "DECSTR"),  /* soft reset */
      |          ^~~~~~~~~

Obtained from: https://invisible-island.net/archives/ncurses/6.5/ncurses-6.5-20241207.patch.gz
MFC after: 3 days