Specify Target Framework for .NET libraries

Having this .csproj in my .NET library will try to update the dependencies that target netstandard2.0, which I don't want to do because then the library would lose back-compat with older versions of AspNetCore.

<ItemGroup Condition="$(TargetFramework) == 'netstandard2.0'">
    <PackageReference Include="Microsoft.AspNetCore.Http.Abstractions" Version="2.2.0" />
    <PackageReference Include="Microsoft.Extensions.Caching.Abstractions" Version="2.2.0" />
    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="2.2.0" />
    <PackageReference Include="Microsoft.Extensions.Options" Version="2.2.0" />
    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
</ItemGroup>
  
<ItemGroup Condition="$(TargetFramework) == 'netcoreapp3.1'">
    <PackageReference Include="Microsoft.Extensions.Caching.Abstractions" Version="3.1.9" />
    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="3.1.9" />
    <PackageReference Include="Microsoft.Extensions.Options" Version="3.1.9" />
    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
</ItemGroup>

It would be really helpful if there was a way to tell dependabot to only look for and update the dependencies in the netcoreapp3.1 target framework.
Is there a way to achieve this?

Start by reproducing the dependency update behavior with the .csproj example and its netstandard2.0 and netcoreapp3.1 target frameworks. Trace Dependabot's .NET dependency handling to determine where target-framework filtering belongs; done means dependencies are updated only for netcoreapp3.1 without changing the netstandard2.0 versions.