Add turn on experimental flag (#2892)

#### Rationale
Fix for the
[ListTest.testMultiChoiceValues](https://teamcity.labkey.org/buildConfiguration/LabkeyTrunk_DailyPostgres_2/3861873?buildTab=tests&status=failed&name=org.labkey.test.tests.list.ListTest.testMultiChoiceValues)

#### Changes
- Turned on experimental flag

Author: DariaBod

src/org/labkey/test/tests/list/ListTest.java

@@ -64,6 +64,7 @@
 import org.labkey.test.util.EscapeUtil;
 import org.labkey.test.util.LogMethod;
 import org.labkey.test.util.Maps;
+import org.labkey.test.util.OptionalFeatureHelper;
 import org.labkey.test.util.PortalHelper;
 import org.labkey.test.util.TestDataGenerator;
 import org.labkey.test.util.TextSearcher;
@@ -1693,6 +1694,7 @@ public void testAutoIncrementKeyEncoded()
     @Test
     public void testMultiChoiceValues()
     {
+        OptionalFeatureHelper.enableOptionalFeature(getCurrentTest().createDefaultConnection(), "multiChoiceDataType");
         Assume.assumeTrue("Multi-choice text fields are only supported on PostgreSQL", WebTestHelper.getDatabaseType() == WebTestHelper.DatabaseType.PostgreSQL);
         // setup a list with an auto-increment key and multi text choice field
         String encodedListName = TestDataGenerator.randomDomainName("multiChoiceList", DomainUtils.DomainKind.IntList);