👷 add C++ standards to macOS matrix #2491

.github/workflows/macos.yml

@@ -13,13 +13,14 @@ jobs:
     strategy:
       matrix:
         xcode: [12.4, 12.3, 12.2, 12.1.1, 12.1, 12, 11.7, 11.6, 11.5, 11.4.1, 11.3.1, 11.2.1, 10.3]
+        standard: [11, 14, 17, 20]
     env:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
 
     steps:
       - uses: actions/checkout@v2
       - name: cmake
-        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON
+        run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DJSON_FastTests=ON -DCMAKE_CXX_STANDARD={{ matrix.standard }} -DCMAKE_CXX_STANDARD_REQUIRED=ON
       - name: build
         run: cmake --build build --parallel 10
       - name: test