fix error message for issue-10176.rs

Author: nikomatsakis

src/test/compile-fail/issue-10176.rs

@@ -12,7 +12,7 @@ fn f() -> isize {
     (return 1, return 2)
 //~^ ERROR mismatched types
 //~| expected type `isize`
-//~| found type `(_, _)`
+//~| found type `(!, !)`
 //~| expected isize, found tuple
 }