Make register job service to be resillient

What does this MR do?

Make scheduler to be resilient to data integrity issues: https://gitlab.com/gitlab-org/gitlab/issues/34897.

This prevents the problem as https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8262 https://gitlab.com/gitlab-org/gitlab/issues/34897.

The scheduler failure is considered retry able, and by default it is retried 2 extra times.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

.gitlab/ci/releases.gitlab-ci.yml

+---
+
+# Syncs any changes pushed to a stable branch to the corresponding CE stable
+# branch. We run this prior to any tests so that random failures don't prevent a
+# sync.
+sync-stable-branch:
+  # We don't need/want any global before/after commands, so we overwrite these
+  # settings.
+  image: alpine:edge
+  stage: sync
+  # This job should only run on EE stable branches on the canonical GitLab.com
+  # repository.
+  only:
+    variables:
+      - $CI_SERVER_HOST == "gitlab.com"
+    refs:
+      - /^[\d-]+-stable-ee$/@gitlab-org/gitlab
+  before_script:
+    - apk add --no-cache --update curl bash
+  after_script: []
+  script:
+    - bash scripts/sync-stable-branch.sh