Migrating Modern Desktop application document is no longer correct

The [Migrating Modern Desktop applications](https://learn.microsoft.com/en-us/dotnet/architecture/modernize-desktop/migrate-modern-applications#migrating-configuration-files) has an example of `` for "system.diagnostics" section that is no longer correct with v7. That section is now implicit and if specified will cause an exception.

The section starts with: "You may come across some issues when using configuration sections that were defined in the machine.config file. For example, consider the following configuration:"

See the breaking change at https://github.com/dotnet/docs/issues/32147

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* ID: 75b9072f-f49f-1997-8c2e-31ef1737581b
* Version Independent ID: 5575fc58-ade8-7771-1133-126ed03c8c2f
* Content: [Migrating Modern Desktop applications](https://learn.microsoft.com/en-us/dotnet/architecture/modernize-desktop/migrate-modern-applications#migrating-configuration-files)
* Content Source: [docs/architecture/modernize-desktop/migrate-modern-applications.md](https://github.com/dotnet/docs/blob/main/docs/architecture/modernize-desktop/migrate-modern-applications.md)
* Product: **dotnet-architecture**
* GitHub Login: @OliaG
* Microsoft Alias: **oliag**