Incompatible pointer types in src/socket.c

[NHOrus]

GCC-14 now enables by default errors for long-deprecated C features.
It causes tinyfugue to fail to build with error:

socket.c: In function ‘handle_socket_lines’:
socket.c:2657:27: error: assignment to ‘String *’ from incompatible pointer type ‘conString *’ [-Wincompatible-pointer-types]
 2657 |             incoming_text = line;
      |                           ^

Gentoo bug: https://bugs.gentoo.org/921030