Added C++23 to CI [skip ci]

Author: ankane

.github/workflows/build.yml

@@ -20,6 +20,10 @@ jobs:
       - run: cmake --build build
       - run: build/test
 
+      - run: cmake -S . -B build -DBUILD_TESTING=ON -DCMAKE_CXX_STANDARD=23
+      - run: cmake --build build
+      - run: build/test
+
       - run: |
           sudo apt-get install valgrind
           valgrind --leak-check=yes build/test