[FLINK-11073] [state backends, tests] Activate ignored testKeyedListS…

…tateSerializerReconfiguration test in StateBackendMigrationTestBase

This test was previously ignored due to 2 missing changes:
- ListSerializerSnapshot was not respecting serializer reconfiguration
  (fixed by FLINK-11073), and
- RocksDBListState did not use the correct registered state serializer
  in backend's state meta info (fixed by FLINK-11287)

With those fixes in, the test can now be activated and expected to pass.

flink-runtime/src/test/java/org/apache/flink/runtime/state/StateBackendMigrationTestBase.java

@@ -40,7 +40,6 @@
 import org.apache.flink.util.TestLogger;
 
 import org.junit.Assert;
-import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
@@ -192,7 +191,6 @@ public void testKeyedListStateMigration() throws Exception {
  }
 
  @Test
- @Ignore("This currently doesn't pass because the ListSerializer doesn't respect the reconfigured case, yet.")
  public void testKeyedListStateSerializerReconfiguration() throws Exception {
  final String stateName = "test-name";