Removed conflict on transaction usage

Author: alex268

jdbc/src/main/java/tech/ydb/jdbc/context/QueryServiceExecutor.java

@@ -255,18 +255,13 @@ public YdbQueryResult executeScanQuery(YdbStatement statement, YdbQuery query, S
                 .withRequestTimeout(scanQueryTimeout)
                 .build();
 
-        if (tx == null) {
-            tx = createNewQuerySession(validator).createNewTransaction(txMode);
-        }
-
+        final QuerySession session = createNewQuerySession(validator);
         String msg = "STREAM_QUERY >>\n" + yql;
         return validator.call(msg, () -> {
-            QueryStream stream = tx.createQuery(yql, isAutoCommit, params, settings);
+            QueryStream stream = session.createQuery(yql, TxMode.SNAPSHOT_RO, params, settings);
             StreamQueryResult result = new StreamQueryResult(msg, statement, query, stream::cancel);
             return result.execute(stream, () -> {
-                if (!tx.isActive()) {
-                    cleanTx();
-                }
+                session.close();
             });
         });
     }

jdbc/src/test/java/tech/ydb/jdbc/impl/YdbQueryPreparedStatementImplTest.java

@@ -350,7 +350,8 @@ public void executeScanQueryAsUpdate() throws SQLException {
             statement.setInt(1, 1);
             statement.setString(2, "value-1");
 
-            statement.executeUpdate();
+            ExceptionAssert.ydbException("Operation 'Upsert' can't be performed in read only transaction",
+                    statement::executeQuery);
         }
     }