Save copy using emplace_back

Co-authored-by: tt4g <45120617+tt4g@users.noreply.github.com>

include/spdlog/details/os-inl.h

@@ -622,7 +622,7 @@ SPDLOG_INLINE std::vector<std::string> get_directory_files(const std::string &di
         if (is_directory)
             continue;
 
-        files.push_back(full_file_name);
+        files.emplace_back(std::move(full_file_name));
     }
 
     closedir(dir);