Cannot update Ponos tasks in the Django admin because a unique constraint is always violated

1. Open any Ponos task in the Django admin.
2. Ensure there is at least one other task with the same run number and slug, in any other process, in the database. This is very common with import, initialisation, thumbnails or docker_build_dockerfile tasks on run 0.
3. Click Save.

4. Please correct the error below.

   Constraint “unique_process_run_slug” is violated.

5. Cry.

This seems to be a very obscure issue with the recent addition of support for arbitrary expressions in UniqueConstraint, and not just database fields. There are now eight ways to express the same constraint:

unique_together = (('process_id', 'run', 'slug'), )
unique_together = (('process', 'run', 'slug'), )
UniqueConstraint('process_id', 'run', 'slug', name='unique_process_run_slug')  # Fails
UniqueConstraint('process', 'run', 'slug', name='unique_process_run_slug')
UniqueConstraint(F('process_id'), F('run'), F('slug'), name='unique_process_run_slug')  # Fails
UniqueConstraint(F('process'), F('run'), F('slug'), name='unique_process_run_slug')
UniqueConstraint(fields=['process_id', 'run', 'slug'], name='unique_process_run_slug')
UniqueConstraint(fields=['process', 'run', 'slug'], name='unique_process_run_slug')

The two failing forms fail because they cause a very strange SQL query:

SELECT 1 AS "a"
FROM "ponos_task"
WHERE (
    "ponos_task"."process_id" = ("ponos_task"."process_id")
    AND "ponos_task"."run" = (0)
    AND "ponos_task"."slug" = ('import')
    AND NOT ("ponos_task"."id" = '5ed033c8-fa2e-4926-b673-3c73c080ff2c'::uuid)
)
LIMIT 1

The process_id = process_id instead of an actual process UUID makes no sense.