querier_cache_test: test_resources_based_cache_eviction: use semaphore::consume() to drain semaphore
querier_cache_test: test_resources_based_cache_eviction: use semaphore::consume() to drain semaphore

It is much more reliable and simple this way, than playing with
`reader_permit::wait_for_admission()`.

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