…on is lower than the minimum. Fixes #21368.

This isn't very user friendly:

    ILLink : unknown error IL7000: An error occurred while executing the custom linker steps. Please review the build log for more information.
    ILLINK : error MT0073: Microsoft.iOS 18.0.8337 does not support a deployment target of 10.0 for iOS (the minimum is 11.0). Please select a newer deployment target in your project's Info.plist or change the SupportedOSPlatformVersion property in your project file.
    ILLINK : error MT2301: The linker step 'Setup' failed during processing: Microsoft.iOS 18.0.8337 does not support a deployment target of 10.0 for iOS (the minimum is 11.0). Please select a newer deployment target in your project's Info.plist or change the SupportedOSPlatformVersion property in your project file.
    [...]/packages/microsoft.net.illink.tasks/8.0.8/build/Microsoft.NET.ILLink.targets(87,5): error NETSDK1144: Optimizing assemblies for size failed. Optimization can be disabled by setting the PublishTrimmed property to false.

So improve this to only show a single error message:

    The SupportedOSPlatformVersion value '10.0' in the project file is lower than the minimum value '11.0'.

Fixes #21368.