tests: Unmark socket-service test as flaky
tests: Unmark socket-service test as flaky

This essentially reverts commit
cffed587371027a1ecc7eba5ad66cb814941785e.

The preceding two commits have fixed the test so it’s no longer flaky.
The following command gives 5000 passes in a row for me:

meson test -C /opt/gnome/build/glib/ socket-service --repeat 5000

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1679

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib