NotificationMessage.target_object_id and source_object_id were typed as
PositiveIntegerField, which overflows when the referenced model uses a
UUID primary key (e.g. MachineConfig). Django's GenericForeignKey stores
the PK as a string in the database, so the field type should be
CharField to accommodate any PK type (int, UUID, slug, etc.).
Changes:
- common/models.py: change target_object_id and source_object_id from
PositiveIntegerField to CharField(max_length=255) on NotificationMessage
- common/migrations/0044: AlterField migration for both columns
- order/tests.py: update assertion from integer 1 to str(1) since
CharField will now store the PK as a string
Fixes#12131
Signed-off-by: kaizeenn <khairil0153@gmail.com>
