SQL: Suppress testShowTablesWorksAsAdmin() tests

These tests are relying on existence of an internal index that might or might not be present when we run this test.

Tracked by elastic/x-pack-elasticsearch#3423

Original commit: elastic/x-pack-elasticsearch@26a7795759

qa/sql/security/src/test/java/org/elasticsearch/xpack/qa/sql/security/SqlSecurityTestCase.java

@@ -334,6 +334,7 @@ public abstract class SqlSecurityTestCase extends ESRestTestCase {
             .assertLogs();
     }
 
+    @AwaitsFix(bugUrl = "https://github.com/elastic/x-pack-elasticsearch/issues/3423")
     public void testShowTablesWorksAsAdmin() throws Exception {
         actions.expectShowTables(Arrays.asList(".security-6", "bort", "test"), null);
         new AuditLogAsserter()