fix: Allow GQL variable definitions in mountFragment

[mike-plummer]

• Fixes component testing failures in SpecsList.cy.tsx

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• Have tests been added/updated?
• Has the original issue (or this PR, if no issue exists) been tagged with a release in ZenHub? (user-facing changes only)
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?

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