sharded: Mark invoke_on_others() helper lambda mutable

Otherwise mutable invoke-on-others lambdas fail to compile

   sharded<foo> f;
   f.invoke_on_others([x] (foo& f) mutable { ... });

generates

/home/xemul/src/seastar/include/seastar/core/future.hh:2074:11: error: no type named ‘type’ in ‘struct std::invoke_result<const invoke_on_modifiers::do_run_test_case() const::<lambda(invoke_on_modifiers::do_run_test_case() const::checker&)>&, invoke_on_modifiers::do_run_test_case() const::checker&>’
 2074 |     using futurator = futurize<std::invoke_result_t<Func, Args&&...>>;
      |           ^~~~~~~~~

The invoke_on_all() has its helper lambda mutable so

    sharded<foo> f;
    f.invoke_on_all([x] (foo& x) mutable { ... });

compiles.

Signed-off-by: Pavel Emelyanov <[email protected]>

include/seastar/core/sharded.hh

@@ -780,7 +780,7 @@ sharded<Service>::invoke_on_others(smp_submit_to_options options, Func func, Arg
  static_assert(std::is_same_v<futurize_t<std::invoke_result_t<Func, Service&, Args...>>, future<>>,
  "invoke_on_others()'s func must return void or future<>");
  try {
- return invoke_on_all(options, [orig = this_shard_id(), func = std::move(func), args = std::tuple(std::move(args)...)] (Service& s) -> future<> {
+ return invoke_on_all(options, [orig = this_shard_id(), func = std::move(func), args = std::tuple(std::move(args)...)] (Service& s) mutable -> future<> {
  return this_shard_id() == orig ? make_ready_future<>() : futurize_apply(func, std::tuple_cat(std::forward_as_tuple(s), args));;
  });
  } catch (...) {