chore: update codeowners for flink shell integration tests (#2734)

Co-authored-by: Brian Strauch <bstrauch@confluent.io>

.github/CODEOWNERS

@@ -1,3 +1,4 @@
-*                             @confluentinc/cli
-pkg/flink/                    @confluentinc/cloud-surfaces
-pkg/ccloudv2/flink_gateway.go @confluentinc/cloud-surfaces
+*                                @confluentinc/cli
+pkg/flink/                       @confluentinc/cloud-surfaces
+pkg/ccloudv2/flink_gateway.go    @confluentinc/cloud-surfaces
+test/fixures/output/flink/shell/ @confluentinc/cloud-surfaces