Use isolated docker config in test sandbox (#700)

* Introduce DOCKER_CONFIG_FILE in test-suite

* Set DOCKER_CONFIG_FILE in CI

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Co-authored-by: Frederik Ring <frederik.ring@gmail.com>

.github/workflows/test.yml

@@ -23,6 +23,8 @@ jobs:
         uses: docker/setup-buildx-action@v2
 
       - name: Run Tests
+        env:
+          DOCKER_CONFIG_FILE: /home/runner/.docker/config.json
         working-directory: ./test
         run: |
           BUILD_IMAGE=1 ./test.sh