tests: Change test container user to root

See this comment by Adrià for details: ckan/ckan-docker-base#86 (comment).

.github/workflows/test.yml

@@ -61,7 +61,7 @@ jobs:
     - name: Create ckan container
       run: |
         /usr/bin/docker create --name test_ckan --network ${{ job.container.network }} --network-alias ckan \
-          --env-file ${{ github.workspace }}/github-workflow.env \
+          --env-file ${{ github.workspace }}/github-workflow.env --user root \
           -v "/var/run/docker.sock":"/var/run/docker.sock" \
           -v "/home/runner/work":"/__w" -v "/home/runner/work/_temp":"/__w/_temp" \
           -v "/home/runner/work/_actions":"/__w/_actions" -v "/opt/hostedtoolcache":"/__t" \