(perf): use a rvalue cast in func_wrapper (#3966)

* (perf): use an rvalue cast in func_wrapper

* Try to clarify comment

* Fix comment typo

Author: Skylion007

include/pybind11/functional.h

@@ -98,8 +98,8 @@ struct type_caster<std::function<Return(Args...)>> {
             explicit func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
             Return operator()(Args... args) const {
                 gil_scoped_acquire acq;
-                object retval(hfunc.f(std::forward<Args>(args)...));
-                return retval.template cast<Return>();
+                // casts the returned object as a rvalue to the return type
+                return object(hfunc.f(std::forward<Args>(args)...)).template cast<Return>();
             }
         };