SERVER-54874 we modified the ConfigServerCatalogCache to refresh using an aggregation pipeline and snapshot read concern.
However, the ephemeral_for_test_kv_engine storage engine doesn't currently support snapshot read concern (SERVER-48314). The ShardingMongodTestFixture uses the ephimeralForTesting storage engine, so the unit tests that involved refreshing the cache with snapshot read concern would fail. Temporarily, to address this
SERVER-53105 added a flag to avoid using snapshot read concern for the refresh and instead use localReadConcern. This flag is only enabled on unit tests.
This ticket is to remove this flag and use snapshotReadConcern in all cases. This can be done once SERVER-48314 is done. Alternatively, we could consider using the wiredTiger storage engine in ShardingMongodTestFixture.