chore: refresh transaction id in it

Author: diegomarquezp

google/cloud/spanner/integration_tests/client_integration_test.cc

@@ -817,12 +817,13 @@ TEST_F(ClientIntegrationTest, ReadLockModeOptionIsSent) {
          StreamOf<std::tuple<std::int64_t>>(tx_a_read_result)) {
       EXPECT_STATUS_OK(row);
     }
-
     // Now a separate tx "B" will perform a write operation before tx "A" is
     // finished.
     auto tx_b = client_->Commit(mutation_helper("FirstModifiedName"));
     EXPECT_STATUS_OK(tx_b);
 
+    tx_a = MakeReadWriteTransaction(tx_a, Transaction::ReadWriteOptions(read_lock_mode));
+
     // Depending on the read lock mode, the result of the next write operation
     // in tx "A" will vary.
     return client_->Commit(tx_a, mutation_helper("SecondModifiedName"));