docker-compose(deps): Bump greenmail/standalone in /docker/compose

Bumps greenmail/standalone from 2.1.8 to 2.1.9.

---
updated-dependencies:
- dependency-name: greenmail/standalone
  dependency-version: 2.1.9
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

docker/compose/docker-compose.ci-test.yml

@@ -24,7 +24,7 @@ services:
     network_mode: host
     restart: unless-stopped
   greenmail:
-    image: docker.io/greenmail/standalone:2.1.8
+    image: docker.io/greenmail/standalone:2.1.9
     hostname: greenmail
     container_name: greenmail
     environment: