Ambiguous operator== overloads with GCC 13 and C++20

[jwillikers]

When building libsass version 3.6.5 with GCC 13.2.1 and C++20 enabled, there are compiler errors regarding amibuous overloads for operator== member functions in ast_sel_cmp.cpp. The errors are as follows.

/home/jordan/.conan/data/libsass/3.6.5/_/_/build/b9b403c606639d0c440df3dfd255621c158be49e/src/src/ast_sel_cmp.cpp:17:51: error: ambiguous overload for 'operator==' (operand types are 'const Sass::SelectorList' and 'const Sass::List')
   17 |     if (auto l = Cast<List>(&rhs)) { return *this == *l; }
      |                                             ~~~~~ ^~ ~~
      |                                             |        |
      |                                             |        const Sass::List
      |                                             const Sass::SelectorList

/home/jordan/.conan/data/libsass/3.6.5/_/_/build/b9b403c606639d0c440df3dfd255621c158be49e/src/src/ast_sel_cmp.cpp:30:54: error: ambiguous overload for 'operator==' (operand types are 'const Sass::SelectorList' and 'const Sass::List')
   30 |     if (auto list = Cast<List>(&rhs)) { return *this == *list; }
      |                                                ~~~~~ ^~ ~~~~~
      |                                                |        |
      |                                                |        const Sass::List
      |                                                const Sass::SelectorList

/home/jordan/.conan/data/libsass/3.6.5/_/_/build/b9b403c606639d0c440df3dfd255621c158be49e/src/src/ast_sel_cmp.cpp:167:20: error: ambiguous overload for 'operator==' (operand types are 'Sass::SelectorComponent' and 'const Sass::SimpleSelector')
  167 |     return *get(0) == rhs;
      |            ~~~~~~~ ^~ ~~~
      |            |          |
      |            |          const Sass::SimpleSelector
      |            Sass::SelectorComponent

/home/jordan/.conan/data/libsass/3.6.5/_/_/build/b9b403c606639d0c440df3dfd255621c158be49e/src/src/ast_sel_cmp.cpp:286:18: error: ambiguous overload for 'operator==' (operand types are 'const Sass::SimpleSelector' and 'Sass::SelectorComponent')
  286 |     return *this == *rhs.get(0);
      |            ~~~~~ ^~ ~~~~~~~~~~~
      |            |        |
      |            |        Sass::SelectorComponent
      |            const Sass::SimpleSelector