cache_hitrate_calculator: fix use after free in non_system_filter lambda
cache_hitrate_calculator: fix use after free in non_system_filter lambda

non_system_filter lambda is defined static which means it is initialized
only once, so the 'this' that is will capture will belong to a shard
where the function runs first. During service destruction the function
may run on different shard and access already other's shard service that
may be already freed.

Fixed #4425

Message-Id: <1b9c39af072fc8180d66de2a43be91ba3a3356f7@scylladb.com>

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