common: Explicitly depend on gio-unix-2.0
This fixes the following on NixOS:
xfce-notify-log-util.c:40:10: fatal error: gio/gdesktopappinfo.h: No such file or directory
40 | #include <gio/gdesktopappinfo.h>
| ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
The reason here is the same as xfce/xfce4-session!51 (merged).