Add XML model with enum property test case

[Copilot]

Adds test coverage for XML payloads containing models with enum properties to packages/http-specs/specs/payload/xml.

Changes

• New model type: ModelWithEnum with single status property of extensible union type
• Enum definition: Status union with "pending", "success", "error" variants
• Operations: GET/PUT endpoints at /payload/xml/modelWithEnum
• Mock API: Scenario handlers for both operations with "success" status value

Example payload

<ModelWithEnum>
  <status>success</status>
</ModelWithEnum>

The extensible union allows any string value beyond the defined variants, following TypeSpec's standard enum pattern.

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• telemetry.astro.build
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/typespec/typespec/website/node_modules/.bin/../astro/astro.js build node s/.b�� tput-dir ../../website/src/conte--llmstxt node /.bin/sh --no-emit tsconfig.build.j/home/REDACTED/work/typespec/typespec/packages/http-specs/node_modules�� st/node-gyp-bin/generate-scenarios-summary sh -c lmstxt --output-dir ../../websit--output-dir sh (dns block)

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>[specs] New test case for XML model with enum property</issue_title>
<issue_description>We need a new test case in https://github.com/microsoft/typespec/blob/main/packages/http-specs/specs/payload/xml/main.tsp to cover the scenario of an XML payload that is a model with a single property defined as an enum.
A possible example payload could look like:

<ModelWithEnum>
    <status>success</status>
</ModelWithEnum>

Where "status" is an extensible union with the following values: "pending", "success", "error".
The scenario should support both GET and PUT operations.

NOTE:

• DO add changelog in https://github.com/microsoft/typespec/tree/main/.chronus/changes
• DO run command

  typespec/packages/http-specs/package.json

  Line 14 in 664978b

  "ci": "prettier specs --write && pnpm validate:all",

  under https://github.com/microsoft/typespec/blob/main/packages/http-specs to check all ci items.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [specs] New test case for XML model with enum property #9659

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