Bump NLog.Extensions.Logging from 5.3.14 to 5.3.15 in /src #5777

Job	Run time
db-container	0s
Windows-Default	13m 52s
Windows-SqlServer	9m 21s
containers	0s
windows-installers	0s
Windows-AzureServiceBus	10m 39s
Windows-RabbitMQ	4m 27s
Windows-AzureStorageQueues	6m 18s
Windows-MSMQ	4m 13s
Windows-SQS	6m 28s
Windows-PrimaryRavenAcceptance	12m 42s
Windows-PrimaryRavenPersistence	6m 48s
Windows-PostgreSQL	4m 39s
Linux-Default	10m 5s
Linux-SqlServer	3m 58s
Linux-AzureServiceBus	9m 29s
Linux-RabbitMQ	3m 57s
container-test	0s
Linux-AzureStorageQueues	3m 37s
Linux-SQS	5m 57s
Linux-PrimaryRavenAcceptance	10m 47s
Linux-PrimaryRavenPersistence	4m 41s
Linux-PostgreSQL	3m 26s
	2h 15m 24s

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