DRIVERS-2921: Use single mongos for unacknowledged write tests (#1595)

cd08b72 added find operations after a w:0 write to ensure it applies, but the client also needs useMultipleMongoses:false to ensure this happens on the same host.

Author: jmikola

source/command-logging-and-monitoring/tests/logging/unacknowledged-write.json

@@ -5,6 +5,7 @@ schemaVersion: "1.16"
 createEntities:
   - client:
       id: &client client
+      useMultipleMongoses: false
       observeLogMessages:
         command: debug
   - database:

source/command-logging-and-monitoring/tests/logging/unacknowledged-write.yml

@@ -5,6 +5,7 @@ schemaVersion: "1.7"
 createEntities:
   - client:
       id: &client client
+      useMultipleMongoses: false
       observeEvents:
         - commandStartedEvent
         - commandSucceededEvent