build: add missing gio-unix-2.0 dependency

Fixes

../src/gmw-main.c:25:10: fatal error: gio/gunixfdlist.h: No such file or directory
 #include <gio/gunixfdlist.h>
          ^~~~~~~~~~~~~~~~~~~
1 job for gio-unix-dep in 3 minutes and 39 seconds (queued for 5 seconds)
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Status Job ID Name Coverage
  Build
passed #17088
build-gnome-multi-writer

00:03:39