[Frontend] [Testing] Unit Testing for mint_certificate transaction builder

[Tybravo]

🎯 Goal

Verify the XDR output of the minting transaction builder.

📋 Requirements

• Implement the feature as described in the goal.
• Ensure integration matches the architecture defined in SUMMARY_TYPESCRIPT.md.
• Handle relevant loading and error states gracefully.

🔧 Technical Scope

• Jest

📂 Affected Path

frontend/hooks/__tests__/useBuildMintTx.test.ts

✅ Acceptance Criteria

• Tests pass in CI.

🔗 PR Requirements

• PR description must include: Closes #[issue_id]