Fix CloneWithUpdatedSource mutating this instead of the clone

[Evangelink]

Fixes #9573

TestMethod.CloneWithUpdatedSource(string source) (and by extension UnitTestElement.CloneWithUpdatedSource) assigned the new source and cleared MethodInfo on this rather than on the returned clone. As a result, the "updated-source" clone kept the old source/MethodInfo, while the shared original element was mutated as a side effect.

Change

var clone = (TestMethod)MemberwiseClone();
clone.AssemblyName = source;   // was: AssemblyName = source;
clone.MethodInfo = null;       // was: MethodInfo = null;
return clone;

UnitTestElement.CloneWithUpdatedSource delegates to this method, so it is fixed transitively.

Build passes with 0 warnings/errors.

[Copilot]

Pull request overview

Fixes an object-model cloning bug in the MSTest adapter platform services layer where TestMethod.CloneWithUpdatedSource mutated the original TestMethod instance instead of the returned clone, causing the clone to retain stale source/MethodInfo while introducing side effects on the shared original.

Changes:

• Update CloneWithUpdatedSource to assign AssemblyName on the cloned instance.
• Update CloneWithUpdatedSource to clear MethodInfo on the cloned instance (not on this).

Show a summary per file

File	Description
src/Adapter/MSTestAdapter.PlatformServices/ObjectModel/TestMethod.cs	Corrects CloneWithUpdatedSource to mutate the clone rather than the original instance.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Low