storage_proxy: Add missing re-throw in truncate_blocking
storage_proxy: Add missing re-throw in truncate_blocking

Iff truncation times out, we want to log it, but the exception should
not be swallowed, but re-thrown.

Fixes #3796.

Message-Id: <90068e0546341c1d7844d4f732004b80324c8c32@scylladb.com>

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