Fixes AD0001 in UNT0038

[sailro]

Fixes #471

Checklist

• I have read the Contribution Guide ;
• There is an approved issue describing the change when contributing a new analyzer or suppressor ;
• I have added tests that prove my fix is effective or that my feature works ;
• I have added necessary documentation (if appropriate) ;

Short description of what this resolves:

Replaced unsafe construct with a proper check.

[Copilot]

Pull request overview

Fixes AD0001 thrown by UNT0038 (CacheYieldInstructionAnalyzer) when a yielded object creation has more than one literal argument. The original code used SingleOrDefault which throws when multiple matching elements exist; the fix restricts analysis to object creations with exactly one argument that is a literal.

Changes:

• Replace SingleOrDefault lookup with explicit "single argument that is a literal" check.
• Add a regression test for yielded constructions with multiple literal arguments.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Microsoft.Unity.Analyzers/CacheYieldInstructionAnalyzer.cs	Replaces unsafe SingleOrDefault predicate with a Count==1 + literal check.
src/Microsoft.Unity.Analyzers.Tests/CacheYieldInstructionAnalyzerTests.cs	Adds regression test reproducing the AD0001 scenario from issue #471.