github: fetch+install subsys again

.github/workflows/cmake-single-platform.yml

@@ -45,6 +45,24 @@ jobs:
       run: cmake --install ${{github.workspace}}/build_indentlog
 
 
+    - name: Clone subsys
+      uses: actions/checkout@v3
+      with:
+        repository: Rconybea/subsys
+        path: repo/subsys
+
+    - name: Configure subsys
+      # configure cmake for subsys in dedicated build directory.
+      run: cmake -B ${{github.workspace}}/build_subsys -DCMAKE_INSTALL_PREFIX=${{github.workspace}}/local repo/subsys
+
+    - name: Build subsys
+      run: cmake --build ${{github.workspace}}/build_subsys --config ${{env.BUILD_TYPE}}
+
+    - name: Install subsys
+      # install into ${{github.workspace}}/local
+      run: cmake --install ${{github.workspace}}/build_subsys
+
+
     - name: Clone refcnt
       uses: actions/checkout@v3
       with: