tests: Disable failure injection around background compactor
tests: Disable failure injection around background compactor

Failure could be injected into the compactor if the main code under
test defers before reaching allocation failure point, and compactor
gets hit. This is not what the test is supposed to stress, and it
causes abort when memtable_snapshot_source is destroyed, so disable
failure injection there.

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