fix(build): BrainScaleS on modern py-pybind11 (another try)
This one includes a fix in hxtorch
that wasn't caught when testing locally (at UHEI) against newer pybind11 versions.
(Same kind of fix: A test binary is built from source files including pybind11 headers w/o using them → in modern pybind11 versions this requires linkage against libpython.)