Migration job fails on a new database
When run on a new database, where the migrations have never been run, the migration script that adds a "force" field fails with:

```
ERROR: 2023-01-31 14:36:28,825 - root - Migration failed: The fields "{'priority'}" do not exist on the document "JobSnapshot"
```

Reported by @rtrompier 
Migration job fails on a new database: When run on a new database, where the migrations have never been run, the migration script that adds a "force" field fails with:

```
ERROR: 2023-01-31 14:36:28,825 - root - Migration failed: The fields "{'priority'}" do not exist on the document "JobSnapshot"
```

Reported by @rtrompier 