According to
https://github.com/MicrosoftDocs/azure-docs/blob/main/includes/app-service-web-configure-robots933456.md

You may see the following message in the container logs:
2019-04-08T14:07:56.641002476Z "-" - - [08/Apr/2019:14:07:56 +0000] "GET /robots933456.txt HTTP/1.1" 404 415 "-" "-"
You can safely ignore this message. /robots933456.txt is a dummy URL path that App Service uses to check if the container is
capable of serving requests. A 404 response simply indicates that the path doesn't exist, but it lets App Service know that
the container is healthy and ready to respond to requests.

But let's rid our logs of errors and warnings