[Bug]: OpenAPI 3.1: Server Variable's default now MUST exist in the enum values, if such values are defined (changed from SHOULD).

[wanlwanl]

Describe the bug

Server Variable's default now MUST exist in the enum values, if such values are defined (changed from SHOULD).
But the default value is always ''

Reproduction

Playground

Checklist

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• The provided reproduction is a minimal reproducible example of the bug.