Fix backtrace/line-tables-only.rs test

The content of the baz function has always been on line 5, not line 15.
Presumably it previously accidentally worked as the call in the foo
function is on line 15, but now it likely tail calls to bar.

Author: bjorn3

tests/ui/backtrace/line-tables-only.rs

@@ -50,5 +50,5 @@ fn main() {
         assert_contains(&backtrace, "foo", "line-tables-only-helper.rs", 5);
     }
     assert_contains(&backtrace, "bar", "line-tables-only-helper.rs", 10);
-    assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 15);
+    assert_contains(&backtrace, "baz", "line-tables-only-helper.rs", 5);
 }