Update seastar submodule
Update seastar submodule

* seastar 8eb6a67a4...166061da3 (3):
  > install-dependencies.sh: add diffutils
  > reactor: replace std::optional (in _network_stack_ready) with compat::optional
  > noncopyable_function: disable -Wuninitialized warning in noncopyable_function_base

Ref #5386.

scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla