try to fix trybuild coverage

Signed-off-by: clux <[email protected]>

Author: clux

kube-derive/tests/ui/union_fails.stderr

@@ -5,8 +5,8 @@ error: Unions can not #[derive(CustomResource)]
   |       ^^^^^^^
 
 error: Serde does not support derive for unions
- --> tests/ui/union_fails.rs:8:1
-  |
+  --> tests/ui/union_fails.rs:8:1
+   |
  8 | / union FooSpec {
  9 | |     int: u32,
 10 | | }