-Wpessimizing-move in min_max

[mborland]

./boost/multiprecision/detail/min_max.hpp:100:26: error: moving a local object in a return statement prevents copy elision [-Werror=pessimizing-move]
  100 |       return std::move(t1);
      |                          ^
./boost/multiprecision/detail/min_max.hpp:100:26: note: remove ‘std::move’ call
./boost/multiprecision/detail/min_max.hpp:101:23: error: moving a local object in a return statement prevents copy elision [-Werror=pessimizing-move]
  101 |    return std::move(t2);
      |                       ^
./boost/multiprecision/detail/min_max.hpp:101:23: note: remove ‘std::move’ call
cc1plus: all warnings being treated as errors

Found while working on odeint here: https://github.com/boostorg/odeint/actions/runs/7259531925/job/19776870666?pr=66#step:10:4092