update nightly test with better json parsing

Author: tylerhutcherson

.github/workflows/nightly-test.yml

@@ -41,8 +41,15 @@ jobs:
           done
 
           NB_JSON=$(printf '%s\n' "${FILTERED_NBS[@]}" | jq -R . | jq -s .)
+
+          # Ensure at least "[]" if empty
+          if [ -z "$NB_JSON" ] || [ "$NB_JSON" = "[]" ]; then
+            NB_JSON="[]"
+          fi
+
           echo "All valid notebooks: $NB_JSON"
-          echo "::set-output name=notebooks::$NB_JSON"
+          echo "notebooks=$NB_JSON" >> $GITHUB_OUTPUT
+
 
   # ---------------------------------------------------------
   # 2) Test all notebooks in parallel