Use mu_ns::isnan rather than sycl::isnan for uniformity.

Author: oleksandr-pavlyk

dpctl/tensor/libtensor/include/kernels/elementwise_functions/isnan.hpp

@@ -79,7 +79,7 @@ template <typename argT, typename resT> struct IsNanFunctor
             return constant_value;
         }
         else {
-            return sycl::isnan(in);
+            return mu_ns::isnan(in);
         }
     }