Change visibility of migration method (#4471)

* change migration visibility

* add empty migration method for 640

---------

Co-authored-by: nathaniel.doef <nathaniel.doef@smilecdr.com>

hapi-fhir-jpaserver-base/src/main/java/ca/uhn/fhir/jpa/migrate/tasks/HapiFhirJpaMigrationTasks.java

@@ -87,9 +87,14 @@ public class HapiFhirJpaMigrationTasks extends BaseMigrationTasks<VersionEnum> {
 		init610();
 		init620();
 		init630();
+		init640();
 	}
 
-	private void init630() {
+	protected void init640() {
+
+	}
+
+	protected void init630() {
 		Builder version = forVersion(VersionEnum.V6_3_0);
 
 		// start forced_id inline migration