Fix stubbed library detection to not require public client ctor (Azure#52043)

Author: JoshLove-msft

eng/packages/http-client-csharp/generator/TestProjects/Spector.Tests/Infrastructure/SpectorTestAttribute.cs

@@ -46,7 +46,6 @@ private static bool IsLibraryStubbed(string clientCsFile)
 
             var constructors = root.DescendantNodes()
                 .OfType<ConstructorDeclarationSyntax>()
-                .Where(c => c.Modifiers.Any(SyntaxKind.PublicKeyword))
                 .ToList();
 
             if (constructors.Count != 0)