Revert "Make work with Java 17"

This reverts commit 2ed3bc4.

Author: vietj

vertx-db2-client/src/test/java/io/vertx/db2client/junit/DB2Resource.java

@@ -30,7 +30,6 @@
 
 import io.vertx.core.net.JksOptions;
 import io.vertx.db2client.DB2ConnectOptions;
-import org.testcontainers.utility.DockerImageName;
 
 public class DB2Resource extends ExternalResource {
 
@@ -46,7 +45,7 @@ public class DB2Resource extends ExternalResource {
     private boolean started = false;
     private boolean isDb2OnZ = false;
     private DB2ConnectOptions options;
-    private final Db2Container instance = new Db2Container(DockerImageName.parse("ibmcom/db2").withTag("11.5.6.0"))
+    private final Db2Container instance = new Db2Container()
             .acceptLicense()
             .withLogConsumer(out -> System.out.print("[DB2] " + out.getUtf8String()))
             .withUsername("vertx")