[ci] try with std 23

Author: ferdymercury

.github/workflows/root-ci.yml

@@ -424,7 +424,7 @@ jobs:
             platform_config: alma10-clang_ninja
             is_special: true
             property: "clang Ninja"
-            overrides: ["CMAKE_CXX_STANDARD=20", "CMAKE_C_COMPILER=clang", "CMAKE_CXX_COMPILER=clang++", "libcxx=ON"]
+            overrides: ["CMAKE_CXX_STANDARD=23", "CMAKE_C_COMPILER=clang", "CMAKE_CXX_COMPILER=clang++", "libcxx=ON"]
             cmake_generator: Ninja
           # Fedora Rawhide with Python debug build
           - image: rawhide