fix(turboquant): restore the stable pin

The bumped fork fails CPU, CUDA, SYCL, ARM64, and gRPC checks. Restore the pin from master until the upstream regression is fixed.

Assisted-by: Codex:gpt-5.4

Author: localai-org-maint-bot

backend/cpp/turboquant/Makefile

@@ -1,7 +1,7 @@
 
 # Pinned to the HEAD of feature/turboquant-kv-cache on https://github.com/TheTom/llama-cpp-turboquant.
 # Auto-bumped nightly by .github/workflows/bump_deps.yaml.
-TURBOQUANT_VERSION?=cd84d316173112e12678485177e420f7e334cb19
+TURBOQUANT_VERSION?=8a891f4b566efdbd3cea92fafee3227a0a267683
 LLAMA_REPO?=https://github.com/TheTom/llama-cpp-turboquant
 
 CMAKE_ARGS?=