Mark test_facet_tags as expected failure on Elasticsearch

wagtail/search/tests/elasticsearch_common_tests.py

@@ -176,3 +176,8 @@ class ElasticsearchCommonSearchBackendTests(BackendTests):
     @unittest.expectedFailure
     def test_incomplete_plain_text(self):
         super().test_incomplete_plain_text()
+
+    @unittest.expectedFailure
+    def test_facet_tags(self):
+        # Failing on Elasticsearch as of #4508
+        super().test_facet_tags()