CI: Set up temporary opt-out Vulkan support (#12614)

Initially Vulkan support in Ollama will require building from source.  Once it is
more thoroughly tested and we have fixed any critical bugs, then we can
bundle Vulkan into the official binary releases.

scripts/build_linux.sh

@@ -13,12 +13,13 @@ set -eu
 . $(dirname $0)/env.sh
 
 mkdir -p dist
+NOVULKAN=${NOVULKAN:-""}
 
 docker buildx build \
         --output type=local,dest=./dist/ \
         --platform=${PLATFORM} \
         ${OLLAMA_COMMON_BUILD_ARGS} \
-        --target archive \
+        --target archive${NOVULKAN} \
         -f Dockerfile \
         .