Dequarantine server_hooks_custom_error_message E2E

What does this MR do?

Similar to !113161 (merged)

Dequarantine server_hooks_custom_error_message_spec to recover coverage for old Web IDE. The test only runs on non-live environments so feature flag toggling is not required at this point. Once the new Web IDE is default enabled, the test can be retired.

Please note that the test can only run against orchestrated environments, more information in gitlab-org/quality/quality-engineering/team-tasks#1621 (comment 1302884549)

E2E Test Failure issue(s)

#387928 (closed)

Check-list

• General code guidelines check-list
  • Code review guidelines
  • Style guides
• Quarantine test check-list
  • Follow the Quarantining Tests guide.
  • Confirm the test has a quarantine: tag with the specified quarantine type.
  • Note if the test should be quarantined for a specific environment.
  • (Optionally) In case of an emergency (e.g. blocked deployments), consider adding labels to pick into auto-deploy (Pick into auto-deploy priority1 severity1).
• Dequarantine test check-list
  • Follow the Dequarantining Tests guide.
  • Confirm the test consistently passes on the target GitLab environment(s).
• To ensure a faster turnaround, ask in the #quality_maintainers Slack channel for someone to review and merge the merge request, rather than assigning it directly.