Update seastar submodule
Update seastar submodule

* seastar 7473945...d6f26d8 (2):
  > semaphore_units: add missing return statement
  > metrics: Do not detroy the metrics layer if it is been used

raphaelsc/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,raphaelsc/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla