Revert skiped test marked as passing test.

Author: WaVEV

django_mongodb/features.py

@@ -206,6 +206,7 @@ def django_test_expected_failures(self):
         "QuerySet.annotate() has some limitations.": {
             # Exists not supported.
             "annotations.tests.NonAggregateAnnotationTestCase.test_annotation_exists_none_query",
+            "lookup.tests.LookupQueryingTests.test_filter_exists_lhs",
             "lookup.tests.LookupTests.test_exact_exists",
             "lookup.tests.LookupTests.test_nested_outerref_lhs",
             "lookup.tests.LookupQueryingTests.test_filter_exists_lhs",