CustomersDot Staging deployment failures are not posted to Slack

Problem

When the deploy-staging job fails for a merge pipeline, an alert is not currently posted to Slack in either #s_fulfillment_staging or #s_fulfillment_status

As an example, https://gitlab.com/gitlab-org/customers-gitlab-com/-/jobs/10956330094 had failed on 2025-08-07 but there were no messages in either Slack channel regarding the deployment failure

However, we can see failed production deployments are still being logged, ex:

Screenshot_2025-08-12_at_7.48.58_AM

Proposal

An alert should be posted to #s_fulfillment_staging if a CustomersDot Staging deployment fails