[Typo] Change parameter used for abstractive summarisation payload

[gn-bcampbell]

Fix Typo

sentenceLength is not supported by Abstractive Summarisation summaryLength should be used instead. This looks to be a typo as it is used only for Extractive Summarisation.

[prmerger-automator]

@gn-bcampbell : 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 2e14d1c:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/ai-services/language-service/summarization/how-to/text-summarization.md	✅Succeeded

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[v-dirichards]

@jboback

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"
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[prmerger-automator]

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

[v-dirichards]

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

@MicrosoftDocs/public-repo-pr-review-team