fix: test sceen validation banner

[ibrahimozkn]

This pull request fixes the issue of the validation banner appearing when the user navigates to the test screen without any defined intervention tasks for the study.

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit faa91bf):

• https://studyu-dev-app--pr671-fix-test-screen-vali-mkerckxd.web.app
• https://studyu-dev-designer--pr671-fix-test-screen-vali-q3t67i3s.web.app

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