ci: build the man page

Author: azmeuk

.github/workflows/tests.yaml

@@ -75,7 +75,8 @@ jobs:
           enable-cache: true
       - name: Install dependencies
         run: uv sync --group doc
-      - run: uv run sphinx-build -W --keep-going doc build/sphinx/html
+      - run: uv run sphinx-build -W --keep-going -b html doc build/sphinx/html
+      - run: uv run sphinx-build -W --keep-going -b man doc build/sphinx/man
 
   bundle:
     runs-on: ubuntu-latest