Remove Shouldly from ProjectCachePlugin sample

[Copilot]

Context

The ProjectCachePlugin sample uses Shouldly (a test assertion library) in production code solely to null-check buildRequest.ProjectInstance. This is an unnecessary dependency for a simple precondition check.

Changes Made

• Replace ShouldNotBeNull() with a plain is null check throwing InvalidOperationException
• Remove using Shouldly; and the Shouldly PackageReference from the project

Testing

Build succeeds with 0 warnings, 0 errors. Behavior is identical — null ProjectInstance still throws with the same message.

Notes

Original prompt

It's silly to use an assertion library in this code just to throw an exception if something is null. Rewrite to equivalent functionality and drop the Shouldly reference from the project file.

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[dotnet-policy-service]

Hello @@copilot, I noticed that you’re changing an .swr file or any file under src/Package/MSBuild.VSSetup.. Please make sure to validate this change by an experimental VS insertion. This is accomplished by pushing to an exp/* branch, which requires write permissions to this repo.

[Copilot]

Pull request overview

This PR removes the Shouldly assertion library from the ProjectCachePlugin sample by replacing its only usage (a null-check on buildRequest.ProjectInstance) with a standard runtime guard and by dropping the Shouldly PackageReference.

Changes:

• Replaced ShouldNotBeNull(...) with an explicit is null check that throws InvalidOperationException
• Removed using Shouldly; from the sample implementation
• Removed the Shouldly PackageReference from the sample project file

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Samples/ProjectCachePlugin/ProjectCachePlugin.csproj	Removes the unused Shouldly dependency from the sample project.
src/Samples/ProjectCachePlugin/AssemblyMockCache.cs	Replaces the Shouldly assertion with a standard null-check + exception.