Mark the headless monitor test as failing

This is failing because I can't figure out
how to make wireplumber and pipewire work
in ci enough to let me add a new monitor :(

As usual, the test works fine locally.

testsuite/headless/meson.build

@@ -8,7 +8,7 @@ env.prepend('MESON_CURRENT_SOURCE_DIR', meson.current_source_dir())
 
 test('monitor',
   find_program('run-headless-monitor-tests.sh', dirs: meson.current_source_dir()),
-  suite: ['headless'],
+  suite: ['headless', 'failing'],
   env: env,
 )