No difference reported for required property changed to optional

Openapi-diff does not report a required property that was changed to optional -- removed from the schema "required" array. Changing a required property to optional in an output schema could cause breaking changes if a client relies on a property always being present in a response (because it was marked "required") and the property is then omitted from some responses in the new version.

Start at the command-line tool's OpenAPI schema comparison and trace how the schema "required" array is handled. Reproduce the reported transition from required to optional in two specifications, then verify that the tool reports the change as breaking.

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