Fix Linux CI CUDA toolkit installation failure

Change cuda-toolkit-12-6 to cuda-toolkit-11-8 which is compatible with manylinux2014 (CentOS 7). The newer CUDA 12.6 package is not available in RHEL7 repositories, causing CI build failures.

Author: bnbailey-psl

.github/workflows/build-wheels.yml

@@ -162,7 +162,7 @@ jobs:
         CIBW_ENVIRONMENT_MACOS: "MACOSX_DEPLOYMENT_TARGET=${{ matrix.arch == 'x86_64' && '13.0' || '14.0' }} CMAKE_OSX_ARCHITECTURES=${{ matrix.arch }} SYSTEM_VERSION_COMPAT=0"
         # Windows/Linux: Include GPU plugins (radiation, energybalance) in addition to visualization
         CIBW_BEFORE_BUILD_WINDOWS: "set CMAKE_RC_COMPILER= && set PYHELIOS_CUDA_ARCHITECTURES=50;60;70;75;80;86;90 && python build_scripts/prepare_wheel.py --buildmode release --plugins weberpenntree,visualizer,photosynthesis,solarposition,stomatalconductance,energybalance,radiation --verbose"
-        CIBW_BEFORE_BUILD_LINUX: "yum install -y zlib-devel mesa-libGL-devel mesa-libEGL-devel libX11-devel libXrandr-devel && yum-config-manager --add-repo https://developer.download.nvidia.com/compute/cuda/repos/rhel7/x86_64/cuda-rhel7.repo && yum install -y cuda-toolkit-12-6 && export PATH=/usr/local/cuda/bin:$PATH && export PYHELIOS_CUDA_ARCHITECTURES='50;60;70;75;80;86;90' && python build_scripts/prepare_wheel.py --buildmode release --plugins weberpenntree,visualizer,photosynthesis,solarposition,stomatalconductance,energybalance,radiation --verbose"
+        CIBW_BEFORE_BUILD_LINUX: "yum install -y zlib-devel mesa-libGL-devel mesa-libEGL-devel libX11-devel libXrandr-devel && yum-config-manager --add-repo https://developer.download.nvidia.com/compute/cuda/repos/rhel7/x86_64/cuda-rhel7.repo && yum install -y cuda-toolkit-11-8 && export PATH=/usr/local/cuda/bin:$PATH && export PYHELIOS_CUDA_ARCHITECTURES='50;60;70;75;80;86;90' && python build_scripts/prepare_wheel.py --buildmode release --plugins weberpenntree,visualizer,photosynthesis,solarposition,stomatalconductance,energybalance,radiation --verbose"
 
         # Manylinux-specific environment for zlib compatibility
         CIBW_ENVIRONMENT_LINUX: "CFLAGS='-D_GNU_SOURCE -I/usr/include' CXXFLAGS='-D_GNU_SOURCE -D_GLIBCXX_USE_CXX11_ABI=0 -I/usr/include' CMAKE_C_FLAGS='-D_GNU_SOURCE' CMAKE_CXX_FLAGS='-D_GNU_SOURCE -D_GLIBCXX_USE_CXX11_ABI=0'"