Use getconf

Author: ankane

.github/workflows/build.yml

@@ -9,19 +9,19 @@ jobs:
         include:
           - ruby: 3.3
             os: ubuntu-24.04
-          - ruby: 3.2
-            os: ubuntu-22.04
-          - ruby: 3.1
-            os: ubuntu-20.04
+          # - ruby: 3.2
+          #   os: ubuntu-22.04
+          # - ruby: 3.1
+          #   os: ubuntu-20.04
           - ruby: 3.2
             os: macos-14
-          - ruby: 3.1
-            os: macos-13
+          # - ruby: 3.1
+          #   os: macos-13
     steps:
       - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
-      - run: MAKE="make -j$(nproc)" bundle exec rake compile
+      - run: MAKE="make -j$(getconf _NPROCESSORS_ONLN)" bundle exec rake compile
       - run: bundle exec rake test