Clean up docker network after run

.gitea/workflows/test-environment.yaml

@@ -12,4 +12,6 @@ jobs:
           sh setup.sh
           sh scripts/get-docker.sh
       - name: Check if Docker was installed         
-        run: docker run hello-world
+        run: docker run hello-world
+      - name: Clean up network (see #3)
+        run: docker network rm main_subnet