CI failure

Some recent change in dune-common leads to issue with executing the python tests in dune-istl. After upgrading to the latest version of dune-common (2c56042598c9895025db4c82fdd83bf36206741f) I can reproduce the problem locally:

make target_pybcrsmatrix
Scanning dependencies of target target_pybcrsmatrix
/bin/sh: 1: bcrsmatrix.py: not found

The problem appears after regenerating the build directory for dune-common, i.e., just pulling in dune-common and calling make in the build directory does not produce the same problem. Something in the CMake configuration must be broken.