shell quoting and variable interpolation issues in the curl command

.forgejo/workflows/auto-update-pr.yaml

@@ -50,16 +50,27 @@ jobs:
         if: steps.changes.outputs.changed == 'true'
         env:
           FORGEJO_TOKEN: ${{ secrets.FORGEJO_TOKEN }}
+          BRANCH_NAME: ${{ steps.commit.outputs.branch_name }}
+          API_URL: ${{ forgejo.api_url }}
+          REPO: ${{ forgejo.repository }}
         run: |
           DATE=$(date +%Y-%m-%d)
+          TIMESTAMP=$(date -Iseconds)
+          
+          cat > /tmp/pr-payload.json << EOF
+          {
+            "title": "chore: weekly flake update ${DATE}",
+            "body": "Automated flake update from CI.\n\nThis PR updates all flake inputs.\n\n**Note:** Build verification will run automatically on this PR.\n\nGenerated on: ${TIMESTAMP}",
+            "head": "${BRANCH_NAME}",
+            "base": "master"
+          }
+          EOF
+          
+          echo "Creating PR with payload:"
+          cat /tmp/pr-payload.json
           
           curl -X POST \
             -H "Authorization: token $FORGEJO_TOKEN" \
             -H "Content-Type: application/json" \
-            -d '{
-              "title": "chore: weekly flake update '"$DATE"'",
-              "body": "Automated flake update from CI.\n\nThis PR updates all flake inputs.\n\n**Note:** Build verification will run automatically on this PR.\n\nGenerated on: '"$(date -Iseconds)"'",
-              "head": "'"${{ steps.commit.outputs.branch_name }}"'",
-              "base": "master"
-            }' \
-            "${{ forgejo.api_url }}/repos/${{ forgejo.repository }}/pulls"
+            -d @/tmp/pr-payload.json \
+            "${API_URL}/repos/${REPO}/pulls"