Preserve log and err on traceback.

Author: rossbar

.github/workflows/ci.yml

@@ -109,4 +109,4 @@ jobs:
     - name: Setup environment
       run: pip install -r requirements.txt
     - name: Build site with execution
-      run: myst build --execute 2>&1 | grep -e "Traceback \(most recent call last\)"
+      run: myst build --execute 2>&1 |tee /dev/stderr | grep -e "Traceback \(most recent call last\)"