Added wait to avoid dangling host_task

Author: oleksandr-pavlyk

dpctl/tensor/_elementwise_common.py

@@ -86,6 +86,7 @@ def __call__(self, x, order="K"):
             r = dpt.empty_like(buf, dtype=res_dt, order=order)
 
         ht, _ = self.unary_fn_(buf, r, sycl_queue=exec_q, depends=[copy_ev])
+        ht_copy_ev.wait()
         ht.wait()
 
         return r