[CI/Build] Refactor Attention backend for test_prefix_prefill from xformers to SDPA#28424

DarkLight1337 merged 3 commits intovllm-project:mainvllm-project/vllm:mainfrom

zhewenl:refactor-test-prefix-prefillzhewenl/vllm:refactor-test-prefix-prefillCopy head branch name to clipboard