Update to MariaDB 10.4 in flyway epp test

Author: onobc

spring-cloud-dataflow-server-core/src/test/java/org/springframework/cloud/dataflow/server/config/FlywayVendorReplacingEnvironmentPostProcessorTests.java

@@ -38,7 +38,7 @@
 public class FlywayVendorReplacingEnvironmentPostProcessorTests {
 
 	@Container
-	private static final MariaDBContainer<?> MARIADB_CONTAINER = new MariaDBContainer<>("mariadb:10.3.6")
+	private static final MariaDBContainer<?> MARIADB_CONTAINER = new MariaDBContainer<>("mariadb:10.4")
 			.withDatabaseName("dataflow")
 			.withUsername("spring")
 			.withPassword("spring");