correctly set preview-url

Author: lukqw

.github/workflows/preview.yml

@@ -35,5 +35,5 @@ jobs:
             make bootstrap-frontend;
             make deploy-frontend;
             distributionId=$(awslocal cloudfront list-distributions | jq -r '.DistributionList.Items[0].Id');
-            echo \"PREVIEW_URL=$AWS_ENDPOINT_URL/cloudfront/$distributionId/\" >> $GITHUB_ENV;
+            echo LS_PREVIEW_URL=$AWS_ENDPOINT_URL/cloudfront/$distributionId/ >> $GITHUB_ENV;