[CI/Build] Replace wikipedia url with local server ones

[Isotr0py]

Purpose

• Fix flaky entrypoints/openai/test_metrics.py::test_metrics_exist[-multimodal] test (https://buildkite.com/vllm/ci/builds/39344/steps/canvas?jid=019a951c-ed1d-4bd1-a6a9-4a92c2fc3ecd):

FAILED entrypoints/openai/test_metrics.py::test_metrics_exist[-multimodal] - openai.InternalServerError: Error code: 500 - {'error': {'message': "403, message='Forbidden', url='https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg'", 'type': 'Internal Server Error', 'param': None, 'code': 500}} 

Test Plan

pytest -s -v tests/entrypoints/openai/test_metrics.py::test_metrics_exist[-multimodal] 

Test Result

Test should use image on s3 now.

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request effectively resolves a flaky test by replacing a dependency on an external Wikipedia URL with a local asset server. This is a good practice that enhances test reliability. The changes are clear, concise, and correctly implemented. I have no further suggestions for improvement.

[DarkLight1337]

Thanks for fixing!