Add a CI job checking that the docs site builds

.github/workflows/ci.yml

@@ -1,7 +1,9 @@
 name: CI
-
-on: [push, pull_request]
-
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 6 * * 6'
 jobs:
   test:
     strategy:

.github/workflows/docs.yml

@@ -0,0 +1,20 @@
+name: Docs
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 6 * * 6'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Download source
+        uses: actions/checkout@v4
+      - name: Install Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+      - name: Install dependencies
+        run: pip install --no-deps -r requirements/requirements-docs.txt
+      - name: Build site
+        run: mkdocs build --strict