ci: resolves wrong context being used by docker build workflow

Author: Sandro Lange

.github/workflows/docker-build.yml

@@ -37,7 +37,8 @@ jobs:
       - name: Build and push
         uses: docker/build-push-action@v5
         with:
-          context: .
+          context: ./ExportPaperless
+          file: ./ExportPaperless/Dockerfile
           push: true
           platforms: linux/amd64,linux/arm64
           tags: |