release-23.1: roachtest: Fix npgsql test

One more npgsql test is flaking on 23.1 due to
#108414.
Marking it as a flake to resolve the failure.

Epic: none
Release note: None
Release justication: Low risk test only change

pkg/cmd/roachtest/tests/npgsql_blocklist.go

@@ -790,4 +790,5 @@ var npgsqlIgnoreList = blocklist{
 	`Npgsql.Tests.TransactionTests(NonMultiplexing).CommitAsync(Prepared)`:                                 "flaky",
 	`Npgsql.Tests.TransactionTests(NonMultiplexing).Rollback(Prepared)`:                                    "flaky",
 	`Npgsql.Tests.TransactionTests(NonMultiplexing).RollbackAsync(NotPrepared)`:                            "flaky",
+	`Npgsql.Tests.CommandTests(Multiplexing).Batched_big_statements_do_not_deadlock`:                       "flaky",
 }