docker-compose: bump confluentinc/cp-kafka from 7.6.1 to 7.9.1 in /test

Bumps confluentinc/cp-kafka from 7.6.1 to 7.9.1.

---
updated-dependencies:
- dependency-name: confluentinc/cp-kafka
  dependency-version: 7.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

test/compose-schemaregistry.yaml

@@ -8,7 +8,7 @@ services:
       - confluent
 
   kafka:
-    image: confluentinc/cp-kafka:7.6.1
+    image: confluentinc/cp-kafka:7.9.1
     environment:
       KAFKA_BROKER_ID: '0'
       KAFKA_ZOOKEEPER_CONNECT: 'zookeeper:2181'