Fix IsolationLevel bugs (#6659)

* Fix `IsolationLevel` bugs

* Revert changes to `DeleteBatchAsync`

Author: Arkatufus

src/contrib/persistence/Akka.Persistence.Sql.Common/Journal/BatchingSqlJournal.cs

@@ -402,7 +402,6 @@ protected BatchingSqlJournalSetup(
             ConnectionTimeout = connectionTimeout;
             WriteIsolationLevel = writeIsolationLevel;
             ReadIsolationLevel = readIsolationLevel;
-            ReadIsolationLevel = writeIsolationLevel;
             CircuitBreakerSettings = circuitBreakerSettings;
             ReplayFilterSettings = replayFilterSettings;
             NamingConventions = namingConventions;