:construction_worker: build ci_module_cpp20 with MSVC

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/windows.yml

diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 124b089..cf0833b 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -111,3 +111,11 @@
         run: cmake --build build --config Debug --parallel 10
       - name: Test
         run: cd build ; ctest -j 10 -C Debug --exclude-regex "test-unicode" --output-on-failure
+
+  ci_module_cpp20:
+    runs-on: windows-latest
+    steps:
+      - name: Run CMake (Debug)
+        run: cmake -S . -B build -G "Visual Studio 17 2022" -DJSON_CI=ON -DCMAKE_CXX_FLAGS="/permissive- /std:c++latest /utf-8 /W4 /WX"
+      - name: Build
+        run: cmake --build build --config Debug --target ci_module_cpp20