add clang-20 (#52)

Author: liss-h

.github/actions/setup_apt/action.yml

@@ -11,6 +11,10 @@ runs:
         # clang-19
         echo "deb http://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-19 main" | sudo tee /etc/apt/sources.list.d/llvm-19.list
         curl https://apt.llvm.org/llvm-snapshot.gpg.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/llvm-19.gpg > /dev/null
+        
+        # clang-20
+        echo "deb http://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-20 main" | sudo tee /etc/apt/sources.list.d/llvm-20.list
+        curl https://apt.llvm.org/llvm-snapshot.gpg.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/llvm-20.gpg > /dev/null
        
         if [[ "$UBUNTU_CODENAME" == "jammy" ]]; then
           # gcc-13