CI: Avoid hitting Dockerhub rate limits

Running the hello-world container from Dockerhub at the beginning of
workflows can cause us to hit rate limits. Switch to a simple docker ps.

Author: markgoddard

.github/workflows/stackhpc-all-in-one.yml

@@ -86,9 +86,9 @@ jobs:
         with:
            submodules: true
 
-      - name: Make sure dockerd is running and test Docker.
+      - name: Make sure dockerd is running and test Docker
         run: |
-          docker run --rm hello-world
+          docker ps
 
       - name: Output image tag
         id: image_tag

.github/workflows/stackhpc-container-image-build.yml

@@ -125,7 +125,7 @@ jobs:
 
       - name: Make sure dockerd is running and test Docker
         run: |
-          docker run --rm hello-world
+          docker ps
 
       - name: Install Kayobe
         run: |