[SYCL] Adjust additional test for clang verification

The names of classes is now emitted fully qualified, so test expected errors needed to adjust

sycl/test/basic_tests/vectors/ctad_fail.cpp

@@ -2,5 +2,5 @@
 #include <sycl/sycl.hpp>
 
 int main() {
-  sycl::vec v(1, .1); // expected-error {{no viable constructor or deduction guide for deduction of template arguments of 'vec'}}
+  sycl::vec v(1, .1); // expected-error {{no viable constructor or deduction guide for deduction of template arguments of 'sycl::vec'}}
 }