remove Clang 15 from CI

Author: soheilshahrouz

.github/workflows/test.yml

@@ -439,7 +439,6 @@ jobs:
         - { name: 'GCC 11 (Ubuntu Noble - 24.04)',    eval: 'CC=gcc-11 && CXX=g++-11',           }
         - { name: 'GCC 12 (Ubuntu Noble - 24.04)',    eval: 'CC=gcc-12 && CXX=g++-12',         }
         - { name: 'GCC 14 (Ubuntu Noble - 24.04)',    eval: 'CC=gcc-14 && CXX=g++-14',         }
-        - { name: 'Clang 15 (Ubuntu Noble - 24.04)',  eval: 'CC=clang-15 && CXX=clang++-15',   }
         - { name: 'Clang 16 (Ubuntu Noble - 24.04)',  eval: 'CC=clang-16 && CXX=clang++-16',   }
         - { name: 'Clang 17 (Ubuntu Noble - 24.04)',  eval: 'CC=clang-17 && CXX=clang++-17',   }
         - { name: 'Clang 18 (Ubuntu Noble - 24.04)',  eval: 'CC=clang-18 && CXX=clang++-18',   }