Update schema in fedramp-ssp-example.oscal.xml

[DimitriZhurkin]

Committer Notes

In fedramp-ssp-example.oscal.xml, update schema to https://github.com/usnistgov/OSCAL/releases/download/v1.1.3/oscal_ssp_schema.xsd.

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• If applicable, does this PR reference the issue it addresses and explain how it addresses the issue?
• If applicable, have all FedRAMP Documents Related to OSCAL Adoption affected by the changes in this issue have been updated? This a chore backlog item that does not require documentation.

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