Stop using deprecated set-output command in workflows

DEV-1359

GitHub actions has deprecated set-output and save-state commands.

https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Author: markgoddard

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

@@ -176,7 +176,7 @@ jobs:
           ssh_key="${ssh_key//$'\n'/'%0A'}"
           ssh_key="${ssh_key//$'\r'/'%0D'}"
           echo "::add-mask::$ssh_key"
-          echo "::set-output name=ssh_key::$ssh_key"
+          echo "ssh_key=$ssh_key" >> $GITHUB_OUTPUT
 
       # The same tag may be reused (e.g. pr-123), so ensure we have the latest image.
       - name: Pull latest Kayobe image