Add missing test dir

Author: tintou

.github/workflows/test.yml

@@ -38,5 +38,5 @@ jobs:
         run: |
           export XDG_RUNTIME_DIR="$(mktemp --tmpdir -d xdg-runtime-XXXXXX)"
           weston --backend=headless --socket=wayland-1 --idle-time=0 &
-          dbus-run-session -- env WAYLAND_DISPLAY=wayland-1 meson test --suite monitor-gui-headless "*:" --print-errorlogs
+          dbus-run-session -- env WAYLAND_DISPLAY=wayland-1 meson test -C build --suite monitor-gui-headless "*:" --print-errorlogs
           # non-headless gui example: meson test -C build --suite monitor "*:" --print-errorlogs