[CI] Fix bake config artifact path for AMI rebuild pipeline (#34656)

Signed-off-by: Amr Mahdi <amrmahdi@meta.com>

.buildkite/image_build/image_build.sh

@@ -151,7 +151,7 @@ print_bake_config() {
     docker buildx bake -f "${VLLM_BAKE_FILE_PATH}" -f "${CI_HCL_PATH}" --print "${TARGET}" | tee "${BAKE_CONFIG_FILE}" || true
     echo "Saved bake config to ${BAKE_CONFIG_FILE}"
     echo "--- :arrow_down: Uploading bake config to Buildkite"
-    buildkite-agent artifact upload "${BAKE_CONFIG_FILE}"
+    (cd "$(dirname "${BAKE_CONFIG_FILE}")" && buildkite-agent artifact upload "$(basename "${BAKE_CONFIG_FILE}")")
 }
 
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