sync_source_enters_quiesce_mode.js has a typo that means this command isn't exercising its write concern.
Fixing the typo does not fix the test, since oplog application will actually hang for the syncSource node on the planExecutorHangBeforeShouldWaitForInserts failpoint when trying to update the replication consistency markers. This means that the write concern for the command is never satisfied (because the primary is disconnected from the syncing node). The original intent of using the failpoint was to hang awaitData queries on the sync source, which would block replication to the syncing node without causing the syncing node to switch its sync source. However, since the failpoint will block replication on the sync source, it isn't helpful for this test.