fix the actual bug

tests/ui/vec.fixed

@@ -217,3 +217,7 @@ fn issue_11958() {
     // should not lint, `String` is not `Copy`
     f(&vec!["test".to_owned(); 2]);
 }
+
+fn issue_12101() {
+    for a in &[1, 2] {}
+}

tests/ui/vec.rs

@@ -217,3 +217,7 @@ fn issue_11958() {
     // should not lint, `String` is not `Copy`
     f(&vec!["test".to_owned(); 2]);
 }
+
+fn issue_12101() {
+    for a in &(vec![1, 2]) {}
+}

tests/ui/vec.stderr

@@ -121,5 +121,11 @@ error: useless use of `vec!`
 LL |     this_macro_doesnt_need_vec!(vec![1]);
    |                                 ^^^^^^^ help: you can use an array directly: `[1]`
 
-error: aborting due to 20 previous errors
+error: useless use of `vec!`
+  --> tests/ui/vec.rs:222:14
+   |
+LL |     for a in &(vec![1, 2]) {}
+   |              ^^^^^^^^^^^^^ help: you can use a slice directly: `&[1, 2]`
+
+error: aborting due to 21 previous errors