fix: adds z-index to modal close button

[pandeymangg]

What does this PR do?

Adds z-index to the modal close button in the survey modal component, fixes the bug that the close button was not clickable.

Fixes # (issue)

How should this be tested?

• Test A
• Test B

Checklist

Required

• Filled out the "How to test" section in this PR
• Read How we Code at Formbricks
• Self-reviewed my own code
• Commented on my code in hard-to-understand bits
• Ran pnpm build
• Checked for warnings, there are none
• Removed all console.logs
• Merged the latest changes from main onto my branch with git pull origin main
• My changes don't cause any responsiveness issues
• First PR at Formbricks? Please sign the CLA! Without it we wont be able to merge it 🙏

Appreciated

• If a UI change was made: Added a screen recording or screenshots to this PR
• Updated the Formbricks Docs if changes were necessary

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1 Ignored Deployment

Name	Status	Preview	Updated (UTC)
formbricks-cloud	⬜️ Ignored (Inspect)		May 3, 2024 9:18am

[github-actions]

Thank you for following the naming conventions for pull request titles! 🙏