Added note about unsupported call

[fikaradz]

Added note about unsupported call

[learn-build-service-prod[bot]]

Learn Build status updates of commit 696217b:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
powerapps-docs/developer/model-driven-apps/clientapi/clientapi-grid-context.md	:white_check_mark:Succeeded

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[JimDaly]

Please apply this change to the internal repo

[JimDaly]

Created #9442 on the internal repo