Use a colon as the version separator in update_system_workers

Closes #1886 (closed)

arkindex/process/management/commands/update_system_workers.py

@@ -245,7 +245,7 @@ class Command(BaseCommand):
         worker_conf = next((worker for worker in data["workers"] if worker["slug"] == slug), None)
         if worker_conf is None:
             raise CommandError(f"No worker with slug {slug} in .arkindex.yml at {url}.")
-        image = f"registry.gitlab.teklia.com/{name}/{version}"
+        image = f"registry.gitlab.teklia.com/{name}:{version}"
         command = worker_conf.get("docker", {}).get("command", None)
         self.update_feature(feature, image=image, command=command, configuration=worker_conf, repo=repo)