preview: Use a different approach to get the PR number

Author: Phantomical

.github/workflows/preview.yml

@@ -20,10 +20,13 @@ jobs:
     steps:
     - name: Get PR number
       id: pr
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       run: |
-        PR_NUMBER="${{ github.event.workflow_run.pull_requests[0].number }}"
-        if [ -z "$PR_NUMBER" ] || [ "$PR_NUMBER" = "0" ]; then
-          echo "No PR number found"
+        PR_NUMBER=$(gh api repos/${{ github.repository }}/pulls \
+          --jq ".[] | select(.head.sha == \"${{ github.event.workflow_run.head_sha }}\") | .number")
+        if [ -z "$PR_NUMBER" ]; then
+          echo "No PR found for SHA ${{ github.event.workflow_run.head_sha }}"
           exit 1
         fi
         echo "number=$PR_NUMBER" >> "$GITHUB_OUTPUT"