The tenant migration hook and fixture implement retryability outside of the driver which is now subtly broken after the PyMongo 4 upgrade.

def _wait_for_reroute_or_test_completion(self, migration_opts):
    start_time = time.time()
    donor_primary = migration_opts.get_donor_primary()

    while not self.__lifecycle.is_test_finished():
        try:
            donor_primary_client = self._create_client(donor_primary)
            ...
        except (pymongo.errors.AutoReconnect, pymongo.errors.NotPrimaryError):
            donor_primary = migration_opts.get_donor_primary()
            continue
        except pymongo.errors.PyMongoError:
            raise
        time.sleep(self.POLL_INTERVAL_SECS)

The above code will select the MongoDFixture of the current primary at operation start, create a client to it, and then attempt to run find commands against it. The change after SERVER-61794 is that a connection to that fixture uses a connection string with directConnection=true in it, disabling any automatic discovery the driver might do. If the selected node fails with a non-retryable error, we will rethrow that error instead of trying to select the primary.

We should remove the custom implementation of retryability, and instead depend on the driver's implementation (which we accidentally already depended on).