Update buildkite plugin docker-compose to v3.9.0

Author: renovate-bot

.buildkite/pipeline.yml

@@ -1,7 +1,7 @@
 steps:
   - label: run bats tests
     plugins:
-      - docker-compose#v3.8.0:
+      - docker-compose#v3.9.0:
           run: tests
 
   - label: run shellcheck