ci: Install markdown-callouts package.

Author: jamesiarmes

.github/workflows/docs.yaml

@@ -21,8 +21,8 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: 3.x
-      - name: Install plantuml
-        run: sudo apt-get update && sudo apt-get install -y plantuml
+      - name: Install packages
+        run: sudo apt-get update && sudo apt-get install -y markdown-callouts plantuml
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
       - uses: actions/cache@v4
         with: