fix(tests): correct expected exception type in PipelineBuilderExceptionTests

- Updated test to expect `TargetInvocationException` instead of `NullReferenceException` for accurate assertion.

Author: holytshirt

test/Paramore.Darker.Tests/PipelineBuilderExceptionTests.cs

@@ -172,7 +172,7 @@ public void ShouldThrowNullReferenceExceptionWhenInnerExceptionIsNull()
             var query = new NullInnerExceptionQuery();
 
             // Act & Assert
-            var exception = Should.Throw<NullReferenceException>(() => _queryProcessor.Execute(query));
+            var exception = Should.Throw<TargetInvocationException>(() => _queryProcessor.Execute(query));
             exception.InnerException.ShouldBeNull();
         }