[FixCI] Enable chunked prefill for auto-prefix-caching test

[MengqingCao]

What this PR does / why we need it?

Enable chunked prefill for auto-prefix-caching test.

After upgrading the vLLM version to v0.11.2 in #4400, the accuracy on auto-prefix-caching + non-chunked-prefill is broken. Due to chunked prefill is enabled by default, we change the apc test case firstly to recover CI.

After vllm-project/vllm#28833, non-Pooling models won't be able to disable chunked prefill any more.
Maybe we should fix the chunked prefill configuration issue in #4498 together

How was this patch tested?

CI passed with existing test.

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[github-actions]

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[gemini-code-assist]

Code Review

This pull request enables chunked prefill for the auto-prefix-caching test to resolve a CI failure, which is a reasonable approach to get the CI passing. The change un-skips a test and updates it to use chunked prefill. My review includes a suggestion to refactor the test to improve maintainability by reducing code duplication, which will make future modifications easier and less prone to error.

[MengqingCao]

@wangxiyuan PTAL

[MengqingCao]

closing as done by #4569