Use most recent version of Eigen library

Author: Eike Mueller

.github/workflows/automated_testing.yml

@@ -20,7 +20,7 @@ jobs:
     - uses: actions/checkout@v3
 
     - name: Download Eigen
-      run: git clone https://gitlab.com/libeigen/eigen.git; cd eigen; git checkout 3.4
+      run: git clone https://gitlab.com/libeigen/eigen.git; cd eigen; git checkout 5.0
 
     - name: Configure Eigen
       working-directory: ${{github.workspace}}/eigen