Update let_unit.fixed

Author: Centri3

tests/ui/let_unit.fixed

@@ -15,11 +15,11 @@ fn main() {
     let _y = 1; // this is fine
     let _z = ((), 1); // this as well
     if true {
+        // do not lint this, since () is explicit
         let _a = ();
     }
-    let a = ();
 
-    // do not lint this
+    // do not lint this, since () is explicit
     let () = dummy();
     let () = ();
     () = dummy();