Update Task adherence prompt to match expected format

[ghyadav]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

If an SDK is being regenerated based on a new swagger spec, a link to the pull request containing these swagger spec changes has been included above.

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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• sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_evaluators/_task_adherence/task_adherence.prompty: Language not supported

[azure-sdk]

API change check

API changes are not detected in this pull request.

[JoseCSantos]

Shall we take the opportunity and update the response schema of task adherence to be json_object like in intent resolution ?