TEST: Fix test for unsigned int bitnot

Author: ubaidsk

integration_tests/test_unary_op_04.py

@@ -1,20 +1,17 @@
-from lpython import u16
+from lpython import u16, bitnot_u16
 
 def foo(grp: u16) -> u16:
-    i: u16 = ~(u16(grp))
-
+    i: u16 = bitnot_u16(grp)
     return i
 
 
 def foo2() -> u16:
-    i: u16 = ~(u16(0xffff))
-
+    i: u16 = bitnot_u16(u16(0xffff))
     return i
 
 def foo3() -> u16:
-    i: u16 = ~(u16(0xffff))
-
-    return ~i
+    i: u16 = bitnot_u16(u16(0xffff))
+    return bitnot_u16(i)
 
 assert foo(u16(0)) == u16(0xffff)
 assert foo(u16(0xffff)) == u16(0)