Check that cmake doc target works in CI

Author: Hannes Steffenhagen

.github/workflows/pull-request-checks.yaml

@@ -66,7 +66,7 @@ jobs:
           # user input
           DEBIAN_FRONTEND: noninteractive
         run: |
-          sudo apt-get install --no-install-recommends -yq cmake ninja-build gcc g++ maven flex bison libxml2-utils dpkg-dev ccache
+          sudo apt-get install --no-install-recommends -yq cmake ninja-build gcc g++ maven flex bison libxml2-utils dpkg-dev ccache doxygen
       - name: Prepare ccache
         uses: actions/cache@v2
         with:
@@ -84,6 +84,10 @@ jobs:
           mkdir build
           cd build
           cmake .. -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER=/usr/bin/gcc -DCMAKE_CXX_COMPILER=/usr/bin/g++
+      - name: Check that doc task works
+        run: |
+          cd build
+          ninja doc
       - name: Zero ccache stats and limit in size
         run: ccache -z --max-size=500M
       - name: Build with Ninja