The NuGet.Client repo currently targets net8.0. For .NET source build, we're updating to use the .NET 9 SDK which requires that NuGet target net9.0.

These are the affected sources that need to be updated:

https://github.com/NuGet/NuGet.Client/blob/39ea8e8081541fb1eb4702a5546e12f81fcad34d/build/common.project.props#L15

https://github.com/NuGet/NuGet.Client/blob/39ea8e8081541fb1eb4702a5546e12f81fcad34d/build/common.targets#L9

https://github.com/NuGet/NuGet.Client/blob/39ea8e8081541fb1eb4702a5546e12f81fcad34d/src/NuGet.Core/NuGet.Configuration/NuGet.Configuration.csproj#L29

https://github.com/NuGet/NuGet.Client/blob/39ea8e8081541fb1eb4702a5546e12f81fcad34d/src/NuGet.Core/NuGet.PackageManagement/NuGet.PackageManagement.csproj#L35