Not able to Build Unit Test Project(.NET 6) in MAC referencing .net standard library(Xamarin Forms) which uses Lottie

## 🐛 Bug Report
dotnet build unit test throwing below error
NETSDK1136: The target platform must be set to Windows (usually by including '-windows' in the TargetFramework property) when using Windows Forms or WPF, or referencing projects or packages that do so.

### Expected behavior
Need to be able to run Unit Test without any errors
### Reproduction steps
In Visual Studio for MAC
Create a new Xamarin Project add Lottie library then create a nunit test project (net6.0 or net7.0) and add Xamarin project reference and try to build to see the issue.
### Configuration

**Version:** 4.0.11 (May be other versions as well)

**Platform:**
- [ ] :iphone: iOS
- [ ] :robot: Android
- [ ] :checkered_flag: WPF
- [ ] :earth_americas: UWP
- [ ] :apple: MacOS
- [ ] :tv: tvOS
- [X] :monkey: Xamarin.Forms

Start by reproducing the dotnet build in Visual Studio for Mac with a Xamarin.Forms project using Lottie and an NUnit net6.0 or net7.0 test project that references it. Investigate the project or package reference that triggers NETSDK1136. Done means the unit test project builds without that error.

Written by the indexing model from the issue text.