contrib: switch to our Guix container instead of the bundled one

Author: kwvg

.github/workflows/guix-build.yml

@@ -33,25 +33,20 @@ jobs:
       - name: Build Docker image
         uses: docker/build-push-action@v2
         with:
-          context: .
-          file: ./contrib/guix/Dockerfile
+          context: ${{ github.workspace }}
+          build-contexts:
+            - docker_root:${{ github.workspace }}/contrib/guix
+          file: ./contrib/containers/guix/Dockerfile
           load: true
-          tags: alpine-guix:latest
+          tags: guix_ubuntu:latest
           cache-from: type=local,src=/tmp/.buildx-cache
           cache-to: type=local,dest=/tmp/.buildx-cache
 
       - name: Run Guix build
         run: |
           export ADDITIONAL_GUIX_COMMON_FLAGS='--max-jobs=32' && \
-          mkdir -p depends/SDKs && \
-          mkdir -p /tmp/guix-store && \
-          curl -L https://bitcoincore.org/depends-sources/sdks/Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz | tar -xz -C depends/SDKs && \
-          docker run --privileged -d --name guix-daemon --rm -v ${{ github.workspace }}:/dash -w /dash alpine-guix:latest && \
-          docker exec guix-daemon bash -c "\
-          chmod 777 /dash/depends && \
-          git config --global --add safe.directory /dash && \
-          cd /dash && \
-          contrib/guix/guix-build"
+          docker run -d --rm guix_ubuntu:latest && \
+          docker exec guix_ubuntu bash -c "guix-start"
 
       - name: Ensure build passes
         run: |