There is no docker tag in UI, but it exists:

```
docker pull registry.gitlab.com/signald/signald:0.21.0
0.21.0: Pulling from signald/signald
2f42a0d7a7b7: Pull complete 
81c2fb1b6074: Pull complete 
7e8b9a51d6b6: Pull complete 
f6ed8fd77301: Pull complete 
64e6fa036bdc: Pull complete 
5e98b5369603: Pull complete 
f2a9b80dd9fc: Pull complete 
Digest: sha256:201cf93efba689aa0319d2a480deea8ffb7dcdfbda31ea45932fccf4c7626ab9
Status: Downloaded newer image for registry.gitlab.com/signald/signald:0.21.0
registry.gitlab.com/signald/signald:0.21.0
```