CELERYD_CONCURRENCY not correctly used in docker enivroment

Steps to reproduce

1. Set CELERYD_CONCURRENCY environment variable in the docker command line
2. Start docker container
3. ps xawfu | grep celery

What happens?

According to celery doc https://docs.celeryproject.org/en/latest/userguide/configuration.html the concurrency should be adjustable with environment variable CELERYD_CONCURRENCY On my 40 core container, I see 40 workers

What is expected?

Number of workers should be the same as CELERYD_CONCURRENCY

Context

Funkwhale version(s) affected: 0.20