convert const ref to value

clang-tidy wrongly sees an std::move to a const ref parameter and
believes it to be pointless. The copy constructor however is deleted.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/fd_monitor.cpp

@@ -199,7 +199,7 @@ void fd_monitor_t::run_in_background() {
     }
 }
 
-void fd_monitor_t::poke_in_background(const poke_list_t &pokelist) {
+void fd_monitor_t::poke_in_background(poke_list_t pokelist) {
     ASSERT_IS_BACKGROUND_THREAD();
     auto poker = [&pokelist](fd_monitor_item_t &item) {
         int fd = item.fd.fd();