Add OndselSolver as git submodule

also update github actions to pull submodules

.github/workflows/sub_buildUbuntu2004.yml

@@ -73,6 +73,8 @@ jobs:
     steps:
       - name: Checking out source code
         uses: actions/checkout@v3
+        with:
+          submodules: true
       - name: Install FreeCAD dependencies
         run: |
           sudo apt-get update -qq