Fix a very subtle mistake in a ui test.

Author: qnighy

src/test/ui/codemap_tests/overlapping_inherent_impls.stderr

@@ -24,6 +24,7 @@ error[E0592]: duplicate definitions with name `baz`
 ...
 43 |     fn baz(&self) {}
    |     ---------------- other definition for `baz`
+   |
    = note: upstream crates may add new impl for `std::marker::Copy` in future versions
 
 error: aborting due to 3 previous errors