Fix mingw32 CI failure: Workaround: Do not install python-scipy

[rwgk]

Description

Affected:

🐍 3 • windows-latest • mingw32

Last to work: 2024-01-08T13:40:51.1780929Z

First broken: 2024-01-13T19:31:58.0408995Z

Example error:

https://github.com/pybind/pybind11/actions/runs/7514690075/job/20457837110

Installing additional packages through pacman...
  C:\Windows\system32\cmd.exe /D /S /C D:\a\_temp\setup-msys2\msys2.cmd -c "'pacman' '--noconfirm' '-S' '--needed' '--overwrite' '*' 'git' 'mingw-w64-i686-gcc' 'mingw-w64-i686-python-pip' 'mingw-w64-i686-python-numpy' 'mingw-w64-i686-python-scipy' 'mingw-w64-i686-cmake' 'mingw-w64-i686-make' 'mingw-w64-i686-python-pytest' 'mingw-w64-i686-eigen3' 'mingw-w64-i686-boost' 'mingw-w64-i686-catch'"
  error: target not found: mingw-w64-i686-python-scipy
  Error: The process 'C:\Windows\system32\cmd.exe' failed with exit code 1

The solution under this PR is to simply not install python-scipy for mingw32. This is only a very minor loss of test coverage, not worth more effort.

For easy future reference, pytest summaries:

• mingw64:

============================= test session starts =============================
platform win32 -- Python 3.11.7, pytest-7.4.4, pluggy-1.3.0
C++ Info: 13.2.0 C++17 __pybind11_internals_v4_mingw_libstdcpp_cxxabi1018__ PYBIND11_SIMPLE_GIL_MANAGEMENT=False
...
=========================== short test summary info ===========================
SKIPPED [1] ../../tests/test_callbacks.py:213: Current PYBIND11_INTERNALS_VERSION too low
SKIPPED [24] ../../tests/test_chrono.py:78: TZ environment variable only supported on POSIX
SKIPPED [1] ../../tests/test_pytypes.py:416: Not defined: PYBIND11_HANDLE_REF_DEBUG
SKIPPED [1] ../../tests/test_stl.py: no <experimental/optional>
====================== 839 passed, 27 skipped in 28.81s =======================

• mingw32:

============================= test session starts =============================
platform win32 -- Python 3.11.7, pytest-7.4.4, pluggy-1.3.0
C++ Info: 13.2.0 C++17 __pybind11_internals_v4_mingw_libstdcpp_cxxabi1018__ PYBIND11_SIMPLE_GIL_MANAGEMENT=False
...
=========================== short test summary info ===========================
SKIPPED [1] ../../tests/test_buffers.py:58: np.float128 does not exist.
SKIPPED [1] ../../tests/test_buffers.py:58: np.complex256 does not exist.
SKIPPED [1] ../../tests/test_callbacks.py:213: Current PYBIND11_INTERNALS_VERSION too low
SKIPPED [24] ../../tests/test_chrono.py:78: TZ environment variable only supported on POSIX
SKIPPED [1] ../../tests/test_eigen_matrix.py:746: could not import 'scipy': No module named 'scipy'
SKIPPED [1] ../../tests/test_eigen_matrix.py:756: could not import 'scipy': No module named 'scipy'
SKIPPED [1] ../../tests/test_pytypes.py:416: Not defined: PYBIND11_HANDLE_REF_DEBUG
SKIPPED [1] ../../tests/test_stl.py:147: no <experimental/optional>
====================== 835 passed, 31 skipped in 28.45s =======================

Suggested changelog entry:

[rwgk]

Thanks @henryiii!