Avoid using #[derive] in test

As per code review, it is preferred to not use derives in tests that
aren't about them.

Author: meithecatte

tests/ui/closures/2229_closure_analysis/only-inhabited-variant-stable.rs

@@ -3,7 +3,6 @@
 // depending on whether some types are inhabited goes too far, introducing a
 // bunch of headaches without much benefit.
 //@ edition:2021
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
 enum Void {}
 
 pub fn main() {
@@ -19,5 +18,5 @@ pub fn main() {
     };
     f();
     g();
-    assert_eq!(r, Err((1, 2)));
+    assert!(matches!(r, Err((1, 2))));
 }

tests/ui/closures/2229_closure_analysis/only-inhabited-variant-stable.stderr

@@ -1,5 +1,5 @@
 error[E0499]: cannot borrow `r` as mutable more than once at a time
-  --> $DIR/only-inhabited-variant-stable.rs:15:17
+  --> $DIR/only-inhabited-variant-stable.rs:14:17
    |
 LL |     let mut f = || {
    |                 -- first mutable borrow occurs here