Update seastar submodule
Update seastar submodule

* seastar 8f0858cfd7...b515d63735 (2):
  > do_with: replace seastar::apply() calls with std::apply()
  > Merge "Resolve various http fixmes" from Piotr

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