move docker testing image into a support folder

It may be good to separate the Docker test resources into a `support`
folder over `tests`. This can avoid any Python packaging issues when
its looking to capture test data for source builds, and makes life
easier in CI scripts for allow-listing folders specific to extension
building versus other actions (i.e. Docker container building).

Signed-off-by: James Knight <james.d.knight@live.com>

.github/workflows/test-docker-publish.yml

@@ -62,7 +62,7 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           context: .
-          file: ./tests/docker/Dockerfile
+          file: ./support/docker/Dockerfile
           build-args: |
             BUILD_MODE=local
           push: ${{ github.event_name != 'pull_request' }}