Add a myst-build job to ci workflows.

- Fail if tracebacks found in myst execution log.
- Preserve log and err on traceback.

Author: rossbar

.github/workflows/ci.yml

@@ -101,6 +101,7 @@ jobs:
     - name: Build static site
       run: pixi run build
 
+
   pixi_build_wasm:
     name: Build jupyterlite site with pixi
     runs-on: ubuntu-latest
@@ -112,3 +113,19 @@ jobs:
 
     - name: Build jupyterlite site
       run: pixi run build_wasm
+
+  myst_build:
+    name: Build and execute static site with myst
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Setup environment
+      run: pip install -r requirements.txt
+    - name: Build site with execution
+      run: |
+        myst build --execute 2>&1 |tee /tmp/mystbuild.log
+        if grep -q "Traceback .most recent call last." /tmp/mystbuild.log; then
+            exit 1;
+        else
+            exit 0;
+        fi