Fixed sway IPC compile warnings

[zjeffer]

I havent' tested this because I don't use sway, but it's a pretty small change.

Fixes these warnings:

[103/154] Compiling C++ object waybar.p/src_modules_sway_ipc_client.cpp.o
../waybar-hyprland-git/src/modules/sway/ipc/client.cpp: In destructor ‘waybar::modules::sway::Ipc::~Ipc()’:
../waybar-hyprland-git/src/modules/sway/ipc/client.cpp:20:10: warning: ignoring return value of ‘ssize_t write(int, const void*, size_t)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   20 |     write(fd_, "close-sway-ipc", 14);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
../waybar-hyprland-git/src/modules/sway/ipc/client.cpp:25:10: warning: ignoring return value of ‘ssize_t write(int, const void*, size_t)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   25 |     write(fd_event_, "close-sway-ipc", 14);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~