ci: use CIBW_PROJECT_REQUIRES_PYTHON

Author: ntamas

.github/workflows/build.yml

@@ -5,8 +5,8 @@ on: [push, pull_request]
 env:
   CIBW_ENABLE: pypy
   CIBW_ENVIRONMENT_PASS_LINUX: PYTEST_TIMEOUT
+  CIBW_PROJECT_REQUIRES_PYTHON: ">=3.9"
   CIBW_TEST_COMMAND: "cd {project} && pip install --prefer-binary '.[test]' && python -m pytest -v tests"
-  CIBW_SKIP: "cp38-* pp38-*"
   PYTEST_TIMEOUT: 60
 
 jobs:
@@ -24,7 +24,6 @@ jobs:
         env:
           CIBW_BEFORE_BUILD: "yum install -y flex bison libxml2-devel zlib-devel cairo-devel && pip install -U cmake pip setuptools wheel && python setup.py build_c_core"
           CIBW_BUILD: "*-manylinux_x86_64"
-          CIBW_ENABLE: pypy
 
       - name: Build wheels (musllinux)
         uses: pypa/cibuildwheel@v3.0.0
@@ -53,7 +52,6 @@ jobs:
           CIBW_BEFORE_BUILD: "yum install -y flex bison libxml2-devel zlib-devel cairo-devel && pip install -U cmake pip setuptools wheel && python setup.py build_c_core"
           CIBW_ARCHS_LINUX: aarch64
           CIBW_BUILD: "*-manylinux_aarch64"
-          CIBW_ENABLE: pypy
 
       - uses: actions/upload-artifact@v4
         with:
@@ -137,7 +135,6 @@ jobs:
         env:
           CIBW_ARCHS_MACOS: "${{ matrix.wheel_arch }}"
           CIBW_BEFORE_BUILD: "pip install -U setuptools && python setup.py build_c_core"
-          CIBW_ENABLE: pypy
           CIBW_ENVIRONMENT: "LDFLAGS=-L$HOME/local/lib"
           IGRAPH_CMAKE_EXTRA_ARGS: -DCMAKE_OSX_ARCHITECTURES=${{ matrix.cmake_arch }} ${{ matrix.cmake_extra_args }} -DCMAKE_PREFIX_PATH=$HOME/local
 
@@ -243,7 +240,6 @@ jobs:
         env:
           CIBW_BEFORE_BUILD: "pip install -U setuptools && python setup.py build_c_core"
           CIBW_BUILD: "*-${{ matrix.wheel_arch }}"
-          CIBW_ENABLE: pypy
           CIBW_TEST_COMMAND: 'cd /d {project} && pip install --prefer-binary ".[${{ matrix.test_extra }}]" && python -m pytest tests'
           # Skip tests for Python 3.10 onwards because SciPy does not have
           # 32-bit wheels for Windows any more