ci: labels on one line, because act_runner splits on the comma alone

A folded YAML scalar turned the label list into `a, b, c`, and act_runner
splits that on `,` without trimming — so two of the three labels would have
registered with a leading space in their names and matched nothing. Which is a
fifteen-minute confusion: the runner is online, the labels look right in the
UI, and jobs queue forever.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docker-compose.ci.yml

@@ -43,10 +43,9 @@ services:
       #
       # Labels are baked into `./data/.runner` at registration — changing this
       # line later does nothing on its own. See the guide.
-      GITEA_RUNNER_LABELS: >-
-        ubuntu-latest:docker://catthehacker/ubuntu:act-24.04,
-        ubuntu-24.04:docker://catthehacker/ubuntu:act-24.04,
-        ubuntu-22.04:docker://catthehacker/ubuntu:act-22.04
+      # One line, no spaces after the commas: act_runner splits this on `,` and
+      # a stray space becomes part of the next label's name.
+      GITEA_RUNNER_LABELS: "ubuntu-latest:docker://catthehacker/ubuntu:act-24.04,ubuntu-24.04:docker://catthehacker/ubuntu:act-24.04,ubuntu-22.04:docker://catthehacker/ubuntu:act-22.04"
       CONFIG_FILE: /config/config.yaml
 
     volumes: