occ app_api:app:unregister fails if container has already been deleted

[R0Wi]

Describe the bug

If (for some reason) a container is deleted in the background - for example via docker command - the occ app_api:unregister fails with the following message:

Client error: `DELETE http://nextcloud-appapi-dsp:2375/v1.41/containers/nc_app_test-deploy?force=true` resulted in a `404 Not Found` response:
{"message":"No such container: nc_app_test-deploy"}

Steps/Code to Reproduce

1. Deploy a container (for example test-deploy) via Nextcloud
2. Wait until container is up and running
3. Delete the container via docker rm
4. Try to delete the ExApp via mentioned command

Expected Results

If docker answers with a "not found", the container can be safely removed from Nextcloud

If this result is intended, I'm happy to create a PR for it

Actual Results

ExApp will never go

Setup configuration

app_api 32.0.0-dev.2

Nextcloud: 31