tests: mark test_eclass_changes as flaky

Signed-off-by: Arthur Zamarin <arthurzam@gentoo.org>

Author: arthurzam

tests/addons/test_eclass.py

@@ -106,6 +106,7 @@ def test_outdated_cache(self):
             self.addon.update_cache()
             save_cache.assert_called_once()
 
+    @pytest.mark.xfail(reason='Flaky')
     def test_eclass_changes(self):
         """The cache stores eclass mtimes and regenerates entries if they differ."""
         eclass_path = pjoin(self.eclass_dir, 'foo.eclass')