cleanup-self-hosted-runner: avoid deleting VMs that are busy

So far, we avoid deleting VMs when they are too young.

But we can do better than that: since the VMs are intended to host an
ephemeral runner, and that runner is registered with the current
repository, we can have a look whether GitHub says that the runner is
busy. If it is, well, let's leave it a-running!

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/cleanup-self-hosted-runners.yml

@@ -46,6 +46,9 @@ jobs:
               
               if [ "$three_hours_ago" -lt "$vm_creation_time" ]; then
                   echo "The VM ${vm_name} was created less then 3 hours ago and shouldn't be deleted yet. Skipping."
+              elif test true = "$(gh api repos/$GITHUB_REPOSITORY/actions/runners \
+                  --jq '.runners[] | select(.name == "'$vm_name'") | .busy)"; then
+                  echo "The VM ${vm_name} is still busy."
               else
                   echo "The VM ${vm_name} was created more than 3 hours ago and wasn't deleted. Let's do that now."
                   az vm delete -n "$vm_name" -g ${{ secrets.AZURE_RESOURCE_GROUP }} --yes