Bug migrating process instance in 6.7.2

**Describe the bug**
Hi!
I’m using flowable 6.7.2 and looks like there’s a problem migrating process instance from one callActivity to another in this version.
Let’s say, I have a simple model like this one:

After starting the process it goes to “call activity 1”. Inside both callActivities there’s just a single user task. So the main process will stop on “call activity 1” and wait for a user task completion.
Now let’s try to migrate process instance from “call activity 1” to “call activity 2” (same model version).

**Expected behavior**
active token will be moved from “call activity 1” to “call activity 2”, subprocess corresponding to “call activity 1” will be deleted and a new subprocess corresponding to “call activity 2” will be started.
Real behavior: no errors, but process instance has no changes after migration.

**Code**
Here’s the code I’m using for migration:

```java
String pid = "4505147";
String definitionId = "test_migration_bug:4:4505206";
ProcessInstanceMigrationBuilder migrationBuilder = processMigrationService.createProcessInstanceMigrationBuilder();
migrationBuilder.migrateToProcessDefinition(definitionId);
ActivityMigrationMapping currentMapping = ActivityMigrationMapping.createMappingFor("Activity_1ik53m0", "Activity_0jpkzf3");
migrationBuilder.addActivityMigrationMapping(currentMapping);
migrationBuilder.migrate(pid);
```

BPMN model:
```xml

Flow_1x3nwgx



Flow_1atp8ps
Flow_0ti4wed



Flow_1x3nwgx
Flow_0lspzco
Flow_0j97xr8


${true}


${false}



Flow_0lspzco
Flow_1atp8ps


Flow_0j97xr8
Flow_0ti4wed

```

**Additional context**
Flowable 6.7.2, PostgreSQL 13.0, Spring Boot.

Reproduce the migration using ProcessInstanceMigrationBuilder, ActivityMigrationMapping, the shown processMigrationService call, and the BPMN model. Start by checking the migration behavior for the two call activities in Flowable 6.7.2 with PostgreSQL 13.0. Done means the token moves to call activity 2, the first subprocess is deleted, and the second subprocess starts.

索引モデルが issue の本文から書いたものです。