update pybind11 version

[Thomas-Ulrich]

fixes #78

di73yeq4@login04:/hppfs/scratch/0A/di73yeq4/2024-12-05_Mw7_California_Earthquak_nc75095651Solucion_strike_98_200m_o5_casc16_1km> python test.py 
/hppfs/work/pn49ha/di73yeq4/user_spack23.1/linux-sles15-skylake_avx512/easi/pbv-intel-2023.1.0-booysj2/lib/python3.10/site-packages/easilib64/cmake/easi/python_wrapper/easi.cpython-310-x86_64-linux-gnu.so
(24, 8)
{'rho': array([2574.04, 3375.4 ]), 'mu': array([2.57033338e+10, 6.75340885e+10]), 'lambda': array([3.31065303e+10, 8.52995376e+10])}

Note that previously if CMake was finding a version, which was too old, the fetch new version through github was raising:

CMake Error: add_library cannot create ALIAS target "pybind11::pybind11_headers" because another target with the same name already exists.

So I had to update more the CMakeList.txt

and this is about 2.12 being the first release compatible with np2
https://github.com/pybind/pybind11/releases/tag/v2.12.0