Refactor method to retrieve agent's response

[mpapas]

get_last_message_by_role() method sig corrected to reflect latest SDK version.

The method was failing in its original form.

[prmerger-automator]

@mpapas : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit fba59b4:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/ai-foundry/agents/how-to/connected-agents.md	✅Succeeded

For more details, please refer to the build report.

[v-regandowner]

@aahill - Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

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[v-dirichards]

@aahill Could you review this proposed update to your article and enter #sign-off in a comment if it's ready to merge?

Thanks!

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