Wrong template parameter in destructor

[Ricardo Abreu]

Originally posted by @jasonivey in #17 (comment)

There are two errors/warnings which seem to conflict:

• GCC 11 with C++20 enabled gives the error:

  scope_guard/scope_guard.hpp:152:36: error: template-id not allowed for destructor
    152 | sg::detail::scope_guard<Callback>::~scope_guard<Callback>() noexcept
          |                                    ^
  

• Clang 12/13/14 triggers the warning -Wdtor-name:

  warning: ISO C++ requires the name after ‘::~’ to be found in the same scope as the name before ‘::~’
  

  Note: this was (incorrectly) fixed with pull request #10 right before the last release