[build] Suppress NuGet warnings

[jpobst]

Suppress some NuGet warnings:

logcat-parse.csproj

Warning NU1701: Package 'Mono.CSharp 4.0.0.143' was restored using '.NETFramework,Version=v4.6.1, 
.NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, 
.NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8' instead of the project target framework 
'.NETCoreApp,Version=v3.1'. This package may not be fully compatible with your project.

Java.Interop.csproj

Warning NU1702: ProjectReference 'D:\a\1\s\build-tools\jnienv-gen\jnienv-gen.csproj' was resolved using 
'.NETFramework,Version=v4.7.2' instead of the project target framework '.NETStandard,Version=v2.0'. 
This project may not be fully compatible with your project.