Avoid parsing global-ids multiple times

What does this MR do?

This is a small ~backstage backend GraphQL MR which removes some redundant work spotted while debugging a test failure (to which this was irrelevant). This is an incidental improvement, which has no functional change.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

This has no effect on the function of the system.

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

/label ~backstage /label backend /label GraphQL