Running without test.sdk is broken #4875

Running .net test projects without test.sdk package referenced fails with:
Testhost process for source(s) 'S:\t\mstest101\bin\Debug\net9.0\mstest101.dll' exited with error: The specified runtimeconfig.json [C:\Program Files\dotnet\sdk\9.0.100-preview.1.24101.2\testhost-9.0.runtimeconfig.json] does not exist
. Please check the diagnostic logs for more information.

or with

Testhost process for source(s) 'S:\t\mstest101\bin\Debug\net8.0\mstest101.dll' exited with error: Error:
An assembly specified in the application dependencies manifest (mstest101.deps.json) was not found:
package: 'MSTest.TestFramework', version: '3.1.1'
path: 'lib/net6.0/Microsoft.VisualStudio.TestPlatform.TestFramework.dll'
. Please check the diagnostic logs for more information.

Test Run Aborted.

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