remove c++20 in ubuntu 20.04; fixing warnings for C++20 builds

Author: noah1510

.github/workflows/cppDesktop.yaml

@@ -22,6 +22,8 @@ jobs:
             os: "ubuntu-22.04"
           - useMsys: true
             os: "macos-latest"
+          - cppStd: "c++20"
+            os: "ubuntu-20.04"
           - cppStd: "c++23"
             os: "ubuntu-20.04"
           - cppStd: "c++23"

target_data/Cpp/cppDesktop/include/unit_system_20.hpp.template

@@ -66,7 +66,7 @@ namespace sakurajin{
                 template <class scalar_t> requires std::convertible_to<scalar_t, base_type>
                 {{ unit.name }}_t<base_type> operator*(scalar_t scalar) const {
                     return {{ unit.name }}_t<base_type>{value * static_cast<base_type>(scalar), multiplier, offset};
-                };
+                }
 
                 template <class scalar_t> requires std::convertible_to<scalar_t, base_type>
                 void operator*=(scalar_t scalar) { value *= static_cast<base_type>(scalar); }