Install libopenblas-dev to provide system BLAS/LAPACK

The bundled OpenBLAS build fails because its gfortran library search
paths only cover GCC up to version 6. Installing a system BLAS/LAPACK
avoids the fallback entirely.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: andreasnoack

.github/workflows/ci.yml

@@ -45,7 +45,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y ccache mpich libmpich-dev ${{ matrix.packages }}
+          sudo apt-get install -y ccache mpich libmpich-dev libopenblas-dev ${{ matrix.packages }}
 
       - name: Set up ccache
         uses: hendrikmuhs/ccache-action@v1