build base image first

Author: pd0wm

.github/workflows/selfdrive_tests.yaml

@@ -404,7 +404,7 @@ jobs:
         submodules: true
     - name: Build docker container
       run: |
-        docker pull $DOCKER_REGISTRY/$BASE_IMAGE:latest || true
+        eval "$BUILD"
         docker pull $DOCKER_REGISTRY/openpilot-docs:latest || true
         DOCKER_BUILDKIT=1 docker build --cache-from $DOCKER_REGISTRY/openpilot-docs:latest -t $DOCKER_REGISTRY/openpilot-docs:latest -f docs/docker/Dockerfile .
     - name: Push docker container