Simplify pack regression arithmetic

Remove unsigned literal suffixes and the unnecessary cast from the sum reproducer.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jketema

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/test.cpp

@@ -52,7 +52,7 @@ static WithDestructor destructed; // GOOD (destructor has a side effect)
 
 static auto sum(auto... values) // $ SPURIOUS: Alert
 {
-	return (0U + ... + static_cast<unsigned>(values));
+	return (0 + ... + values);
 }
 
-unsigned result = sum() + sum(2U);
+unsigned result = sum() + sum(2);