fix(files): correct Folder required property case

[ryanduguid]

Summary

• correct the case of the Files Folder schema's required property from name to Name
• retain the intended requirement while matching the schema property and documented create/update request bodies

Verification

• parsed the OpenAPI YAML with PyYAML
• validated { "Name": "My Docs" } against Folder with jsonschema
• confirmed an empty Folder still fails with Name required

The documented request body fails on master because the schema requires a nonexistent lower-case name field.

[ryanduguid]

Closing this as part of cleaning up an unsolicited batch I opened across several Xero repositories. I will not reopen unless a maintainer asks for a single focused change.