Fix typo: Usupported Regions -> Unsupported Regions

[changeworld]

[prmerger-automator[bot]]

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

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

Learn Build status updates of commit 05b2932:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
articles/migrate/azure-migrate-unsupported-regions.md	:white_check_mark:Succeeded

For more details, please refer to the build report.

[habibaum]

Reviewed and can be published

[v-dirichards]

@habibaum In the future, when the changes are ready for publication, add a #sign-off comment to signal that the PR is ready for the review team to merge.