Album art not displaying following update to attachments table Amazon S3

Steps to reproduce

1. Upgrade a pod using Amazon S3 as its storage backend to develop image at commit 7c6855d9
2. Navigate to site in browser

What happens?

Album art images are not displayed

What is expected?

Album art should be displayed as normal

Context

Funkwhale version(s) affected: develop: git+7c6855d9

• Browsers tested: Chrome, Firefox
• Instance configuration: Docker multi-container, nginx, Amazon S3 backend
• Error messages: during migration NotImplementedError: This backend doesn't support absolute paths. is encountered (full output below)
• Audio streaming is not impacted

  Applying music.0043_album_cover_attachment...Traceback (most recent call last):
  File "manage.py", line 27, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3.6/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3.6/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python3.6/site-packages/django/core/management/base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/lib/python3.6/site-packages/django/core/management/base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python3.6/site-packages/django/core/management/base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 234, in handle
    fake_initial=fake_initial,
  File "/usr/lib/python3.6/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.6/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.6/site-packages/django/db/migrations/executor.py", line 245, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/usr/lib/python3.6/site-packages/django/db/migrations/migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/usr/lib/python3.6/site-packages/django/db/migrations/operations/special.py", line 190, in database_forwards
    self.code(from_state.apps, schema_editor)
  File "/app/funkwhale_api/music/migrations/0043_album_cover_attachment.py", line 21, in create_attachments
    mimetype=get_mimetype(album.cover.path),
  File "/usr/lib/python3.6/site-packages/django/db/models/fields/files.py", line 57, in path
    return self.storage.path(self.name)
  File "/usr/lib/python3.6/site-packages/django/core/files/storage.py", line 109, in path
    raise NotImplementedError("This backend doesn't support absolute paths.")
NotImplementedError: This backend doesn't support absolute paths.