Upgrade to Mongo 4 in integration tests

Following on from 97fc371

Author: adrianclay

service/src/intTest/java/uk/nhs/adaptors/gp2gp/testcontainers/MongoDbContainer.java

@@ -7,7 +7,7 @@
 @Slf4j
 public final class MongoDbContainer extends GenericContainer<MongoDbContainer> {
     public static final int MONGODB_PORT = 27017;
-    public static final String DEFAULT_IMAGE_AND_TAG = "mongo:3.6.23";
+    public static final String DEFAULT_IMAGE_AND_TAG = "mongo:4.0.28";
     private static MongoDbContainer container;
 
     private MongoDbContainer() {