tests: budget proposal costing and further information validation

[kneerose]

List of changes

• Add validation test for budget proposal further information section
• Add validation test for budget propsal costing section

Checklist

• related issue
• My changes generate no new warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the changelog
• I have added tests that prove my fix is effective or that my feature works

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded

[github-actions]

✅ All checks succeeded

[mesudip]

Looks good