dbcopy: use less fancy time format

This patch replaces "%F %T" with the equivalent (and more portable) long
variant "%Y-%m-%d %H:%M:%S", so that Windows build will show progress,
too.

core/src/dird/dbcopy/progress.cc

@@ -134,7 +134,8 @@ static std::string FormatTime(time_point<system_clock> tp)
   std::time_t time = system_clock::to_time_t(tp);
   std::array<char, Progress::default_timestring_size> buffer{};
 
-  std::strftime(buffer.data(), buffer.size(), "%F %T", std::localtime(&time));
+  std::strftime(buffer.data(), buffer.size(), "%Y-%m-%d %H:%M:%S",
+                std::localtime(&time));
 
   return std::string(buffer.data());
 }