Fix image name syntax in Docker workflow

There has been an additional slash in the docker image name, which lead to an error in the build process.

Author: penguineer

.github/workflows/docker-image.yml

@@ -12,7 +12,7 @@ on:
 
 env:
   REGISTRY: docker.io
-  IMAGE_NAME: ${{ secrets.DOCKERHUB_USERNAME }}//spaceapi-service
+  IMAGE_NAME: ${{ secrets.DOCKERHUB_USERNAME }}/spaceapi-service
   TARGET_PLATFORMS: linux/amd64,linux/arm64,linux/arm/v7
 
 jobs: