[SYCL] Correct misplaced sycl_kernel_entry_point attribute in a namespace declaration of a negative test. (#122375)
Commit 1a73654b3212b623ac21b9deb3aeaadc6906b7e4 added a missing
diagnostic for incorrect placement of an attribute in a namespace
declaration. This change corrects a SYCL test that inadvertently
exercised the `sycl_kernel_entry_point` attribute in the wrong
declaration location.