Update out-of-support net8.0 MAUI targets to net9.0

[edgchen1]

Description

.NET MAUI 8 is out of support. See here: https://dotnet.microsoft.com/en-us/platform/support/policy/maui

We started seeing errors about this in the NuGet packaging pipeline.

##[error]C:\Program Files\dotnet\sdk\9.0.306\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.EolTargetFrameworks.targets(38,5): Error NETSDK1202: The workload 'net8.0-ios' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/maui-support-policy for more information about the support policy.

This change updates net8.0 mobile target framework monikers to net9.0.

Motivation and Context

Fix packaging pipeline.

[snnn]

LGTM. But, actually I am not able to build the code with .net9 on Linux ( I didn't enable mobile). It's due to the *.snk files . The files were generated years ago with a weak RSA key. Now openssl rejects such low-strength RSA algorithms. So, it cannot sign the files. So, dotnet build cannot generate the managed DLLs.

[edgchen1]

LGTM. But, actually I am not able to build the code with .net9 on Linux ( I didn't enable mobile). It's due to the *.snk files . The files were generated years ago with a weak RSA key. Now openssl rejects such low-strength RSA algorithms. So, it cannot sign the files. So, dotnet build cannot generate the managed DLLs.

I suppose we'll have to deal with it when upgrading the other target frameworks to net9.0. currently, only the MAUI net8.0 ones are out of support.