Simplify github actions to use less jobs

[Romfos]

Changed:

• Move target tfms from matrix to steps

Motivation:
Each new test TFM will add +3 new jobs to test matrix (for each OS).
Make sense to run all test for OS in one job

this is part of preparation for adding .NET 10 to test matrix

[Copilot]

Pull Request Overview

This PR simplifies the GitHub Actions test workflow by consolidating multiple jobs into fewer jobs. Instead of using a matrix strategy that creates separate jobs for each OS-framework combination, the workflow now runs all target framework tests as separate steps within each OS job.

• Removed the framework matrix dimension and Windows-specific include configuration
• Added individual test steps for each target framework (.NET Framework 4.6.2, .NET 8, .NET 9)
• Conditional execution for .NET Framework tests only on Windows

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