Add -d flag when spinning up container

.github/workflows/docker.yml

@@ -15,6 +15,6 @@ jobs:
  - name: build image
  run: docker buildx build -t catadog .
  - name: test image by starting up a container
- run: docker run --rm --name catadog catadog
+ run: docker run --rm -d --name catadog catadog
  - name: kill container
  run: docker container kill catadog