Migration critical section for one collection will block finds for any other sharded collection

The find command implementation in 3.2 indiscriminately checks for critical section before even looking at the collection's shard version. This causes the migration critical section on one collection to stall find operations for all other collections even if they do not participate in migrations themselves.

Since in 3.2 there isn't a (non-racy) way to differentiate between the critical sections on one collection versus another, at the very least this check should only be done if shard version mismatch is encountered and not all the time.