appmonitor: Skip the test under OSX

Since commit c0ca3f99 this test is strictly depending on GDesktopAppInfo
that is not defined or available in macos, so skip the test as we do for
windows.

We could have done this at meson level too, but keeping it this way is
probably a better reminder that this should be adapted for such scenario
one day™

See: https://gitlab.gnome.org/GNOME/glib/-/jobs/2753753


(cherry picked from commit d296e94559)

gio/tests/appmonitor.c

@@ -22,7 +22,7 @@
 #include <gio/gio.h>
 #include <gstdio.h>
 
-#ifdef G_OS_UNIX
+#if defined (G_OS_UNIX) && !defined (__APPLE__)
 #include <gio/gdesktopappinfo.h>
 #endif
 
@@ -49,7 +49,7 @@ teardown (Fixture       *fixture,
   g_clear_pointer (&fixture->applications_dir, g_free);
 }
 
-#ifdef G_OS_UNIX
+#if defined (G_OS_UNIX) && !defined (__APPLE__)
 static gboolean
 create_app (gpointer data)
 {
@@ -97,13 +97,13 @@ timeout_cb (gpointer user_data)
 
   return G_SOURCE_REMOVE;
 }
-#endif  /* G_OS_UNIX */
+#endif  /* defined (G_OS_UNIX) && !defined (__APPLE__) */
 
 static void
 test_app_monitor (Fixture       *fixture,
                   gconstpointer  user_data)
 {
-#ifdef G_OS_UNIX
+#if defined (G_OS_UNIX) && !defined (__APPLE__)
   gchar *app_path;
   GAppInfoMonitor *monitor;
   GMainContext *context = NULL;  /* use the global default main context */
@@ -162,9 +162,11 @@ test_app_monitor (Fixture       *fixture,
   g_object_unref (monitor);
 
   g_free (app_path);
-#else  /* if !G_OS_UNIX */
+#elif defined (__APPLE__)
+  g_test_skip (".desktop monitor on macos");
+#else  /* if !(defined (G_OS_UNIX) && !defined (__APPLE__)) */
   g_test_skip (".desktop monitor on win32");
-#endif  /* !G_OS_UNIX */
+#endif  /* !(defined (G_OS_UNIX) && !defined (__APPLE__)) */
 }
 
 int