Back to head ref

Using the potential merge commit doesn't report this PR as being
deployed, so we need to use the head ref. The risk is that this head ref
is behind the base branch, but we have that risk anyway.

Author: cmbuckley

.github/workflows/deploy-preview.yml

@@ -45,12 +45,11 @@ jobs:
           DEPLOY: ${{ github.event.inputs.deploy_id }}
         run: |
           set -e ${RUNNER_DEBUG:+-x}
-          ref=$(gh pr view $ISSUE --json potentialMergeCommit -q .potentialMergeCommit.oid)
-          [ -z "$ref" ] && { echo "No merge commit for PR $ISSUE"; exit; }
 
           env=staging-$ISSUE
           url=https://$env.cmbuckley.co.uk
           echo "url=$url" >> $GITHUB_OUTPUT
+          ref=$(gh pr view $ISSUE --json headRefOid -q .headRefOid)
 
           # create environment unless it exists already
           gh api --silent repos/{owner}/{repo}/environments/$env 2>/dev/null \