Bump Microsoft.Extensions.ServiceDiscovery from 8.2.0 to 8.2.1 in /docs/extensibility/snippets/MailDevResourceWithCredentials/MailDevResource.ServiceDefaults in the dotnet group

Bump Microsoft.Extensions.ServiceDiscovery from 8.2.0 to 8.2.1 in /docs/extensibility/snippets/MailDevResourceWithCredentials/MailDevResource.ServiceDefaults in the dotnet group #2988