Expand EOL list to include net7 6 months after it goes OOS per design

[marcpopMSFT]

Summary

When a version of .NET goes out of support, we add a gold bar in Visual Studio when customers open a project targeting that version and we mark it out of support in the UI. However, to give customers time to migration, we don't mark it as a warning in builds for 6 months as otherwise, customers with warnings as errors would be broken immediately.

Customer Impact

Customers targeting net7.0 will get a warning that the runtime is out of support. They can upgrade, suppress the warning, or set a property to disable the warning.

Regression

Intentional change

Testing

Automated. Had to modify a few tests to remove the net7.0 targeting or disable the warning.

Risk

Low.

[marcpopMSFT]

/backport to release/9.0.1xx

[github-actions]

Started backporting to release/9.0.1xx: https://github.com/dotnet/sdk/actions/runs/10855800411

[marcpopMSFT]

@MichalStrehovsky @LakshanF I went ahead and just disabled the new warning in the two AOT tests that hit net7. Let me know if you've rather just have those tests no longer target net 7. I make the change here and #43441. The plan is to merge for GA.

[dotnet-policy-service]

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

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Tagging @dotnet/compat for awareness of the breaking change.