Merge branch '1160-systemd-fix' into 'develop'

Resolve "funkwhale-worker.service error option --concurrency"

Closes #1160

See merge request funkwhale/funkwhale!1296

(cherry picked from commit 31413fe6)

d3fdce07 Correctly set default value in systemd unit
942d0d14 Add changelog fragment

changes/changelog.d/1160.bugfix

+Fixed systemd unit for funkwhale-worker (#1160)

deploy/funkwhale-worker.service

@@ -7,8 +7,9 @@ PartOf=funkwhale.target
 User=funkwhale
 # adapt this depending on the path of your funkwhale installation
 WorkingDirectory=/srv/funkwhale/api
+Environment="CELERYD_CONCURRENCY=0"
 EnvironmentFile=/srv/funkwhale/config/.env
-ExecStart=/srv/funkwhale/virtualenv/bin/celery -A funkwhale_api.taskapp worker -l INFO --concurrency=${CELERYD_CONCURRENCY-0}
+ExecStart=/srv/funkwhale/virtualenv/bin/celery -A funkwhale_api.taskapp worker -l INFO --concurrency=${CELERYD_CONCURRENCY}
 
 
 [Install]