Clarify which supportedRuntime options should be configured in app.config when <TargetFrameworks> has plural monikers configured

I'm migrating legacy `c#` / `vb` applications to newer frameworks.

I moved project files from legacy project files (`non-SDK`) into modern `SDK` style. Now I also added `net452` and `net481` as options to compile projects to (`net452;net481`).

My question is how to make deal with `supportedRuntime` option in app.config like:

now, this file will be shared between 2 different binaries, what values should I put there (lowest, highest)?

Based on the [doc](https://learn.microsoft.com/en-us/dotnet/framework/configure-apps/file-schema/startup/supportedruntime-element#remarks), there is no way to specify multiple supportedRuntime options for frameworks bigger than 4.0

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* ID: cbaa501d-ecb5-34d9-841f-d858056af103
* Version Independent ID: 5b9d3e55-a6e5-46c7-78d3-fc5f2b3a5bab
* Platform ID: 0e9d47a6-95ec-8937-1f6d-183f3fb36683
* Content: [<supportedRuntime> configuration element - .NET - .NET Framework](https://learn.microsoft.com/en-us/dotnet/framework/configure-apps/file-schema/startup/supportedruntime-element#remarks)
* Content Source: [docs/framework/configure-apps/file-schema/startup/supportedruntime-element.md](https://github.com/dotnet/docs/blob/main/docs/framework/configure-apps/file-schema/startup/supportedruntime-element.md)
* Service: **dotnet-framework**
* GitHub Login: @gewarren
* Microsoft Alias: **dotnetcontent**