EnlistTransaction should not throw when called multiple times with the same transaction

[dennis-gr]

EnlistTransaction should check whether the given transaction is the same as the one it is already enlisted in and do nothing in that case. That would match the behaviour of MySql.Data and other providers.

Test to reproduce:

[Fact]
public void EnlistingInTheSameAmbientTransactionMultipleTimesDoesNotThrow()
{
	using (new TransactionScope())
	{
		using (var connection = new MySqlConnection("AutoEnlist=false"))
		{
			connection.Open();
			
			connection.EnlistTransaction(Transaction.Current);
			connection.EnlistTransaction(Transaction.Current);
		}
	}
}

[bgrainger]

Fixed in 0.50.0.