fix(action): Set entrypoint to bash when retrieving container ID

An image may not define an entrypoint in which case we need to define one

action.yml

@@ -23,7 +23,7 @@ runs:
     - name: Sign kernel
       shell: bash
       run: |
-        CONTAINER_ID=$(podman run --replace --name "${{ inputs.image }}" -dt "${{ inputs.image }}")
+        CONTAINER_ID=$(podman run --entrypoint /bin/bash --replace --name "${{ inputs.image }}" -dt "${{ inputs.image }}")
         podman cp "${{ github.action_path }}"/sign-kernel.sh "${{ inputs.image }}":/tmp/sign-kernel.sh
         podman exec -e PRIVKEY="${{ inputs.privkey }}" -e PUBKEY="${{ inputs.pubkey }}" "${{ inputs.image }}" "/tmp/sign-kernel.sh"
         for TAG in $TAGS; do