Make DebugSqlSpec abstract

It is used for debugging tests and should be kept abstract or
else it violates the naming conventions. It violates the naming
conventions because we do not wish to run it with the normal build.

Original commit: elastic/x-pack-elasticsearch@ce5810b15a

sql/jdbc/src/test/java/org/elasticsearch/xpack/sql/jdbc/DebugSqlSpec.java

@@ -14,7 +14,7 @@ import java.nio.file.Path;
 import java.util.List;
 
 @TestLogging(JdbcTestUtils.SQL_TRACE)
-public class DebugSqlSpec extends SqlSpecIT {
+public abstract class DebugSqlSpec extends SqlSpecIT {
 
     @ParametersFactory(shuffle = false, argumentFormatting = SqlSpecIT.PARAM_FORMATTING)
     public static List<Object[]> readScriptSpec() throws Exception {