moving a temporary object prevents copy elision

[ryandesign]

Building the SDL/scons version on macOS 12.7.2 with clang 17.0.6 (and with -Wextra, if that's relevant) I get several warnings but the most frequent (occurring 110 times due to the many places this file is included) is:

Concurrency/AsyncTaskQueue.hpp:123:14: warning: moving a temporary object prevents copy elision [-Wpessimizing-move]
  123 |                         thread_ = std::move(std::thread{
      |                                   ^
Concurrency/AsyncTaskQueue.hpp:123:14: note: remove std::move call here
  123 |                         thread_ = std::move(std::thread{
      |                                   ^~~~~~~~~~
1 warning generated.