/backport to rel/3.10

Started backporting to rel/3.10: https://github.com/microsoft/testfx/actions/runs/17396351123

I am using VSTest in some projects and I am upgrading from 3.11.0 to 4.0.0 today and got a lot of MSTEST0001 errors.
I could not find this in the release notes for 4.0.0 at https://github.com/microsoft/testfx/releases/tag/v4.0.0

This PR is already part of 3.11.
What probably affects you is that it's now enabled by default. You can turn it off by adding <NoWarn>$(NoWarn);MSTEST0001</NoWarn>, or set it off in .globalconfig, or alternatively keep it on and address the warning.

Can you please add to the v4.0.0 release notes/documentation that it is enabled by default? (so other people also know about this)

It is also not mentioned in the migration guide from v3 to v4 at https://learn.microsoft.com/en-us/dotnet/core/testing/unit-testing-mstest-migration-v3-v4

Updating the migration guide in dotnet/docs#48969