updated flash_attn GIT_TAG to point to torch Stable ABI FA3 commit (#47995)

Signed-off-by: Chris Leonard <chleonar@redhat.com>

Author: cleonard530

cmake/external_projects/vllm_flash_attn.cmake

@@ -39,7 +39,7 @@ else()
   FetchContent_Declare(
           vllm-flash-attn
           GIT_REPOSITORY https://github.com/vllm-project/flash-attention.git
-          GIT_TAG 2c839c33742309ec41e620bf837495ec9926c56e
+          GIT_TAG b3964b1d8b95d8e8447435668ab169a2700bab65
           GIT_PROGRESS TRUE
           # Don't share the vllm-flash-attn build between build types
           BINARY_DIR ${CMAKE_BINARY_DIR}/vllm-flash-attn