Add test for ?const in nested impl/dyn trait

Author: ecstatic-morse

src/test/ui/rfc-2632-const-trait-impl/const-trait-bound-opt-out/in-trait-object.rs

@@ -15,4 +15,8 @@ fn trait_object() -> &'static dyn ?const T { &S }
 //~^ ERROR `?const` is not permitted in trait objects
 //~| ERROR `?const` on trait bounds is not yet implemented
 
+fn trait_object_in_apit(_: impl IntoIterator<Item = Box<dyn ?const T>>) {}
+//~^ ERROR `?const` is not permitted in trait objects
+//~| ERROR `?const` on trait bounds is not yet implemented
+
 fn main() {}

src/test/ui/rfc-2632-const-trait-impl/const-trait-bound-opt-out/in-trait-object.stderr

@@ -10,6 +10,12 @@ error: `?const` is not permitted in trait objects
 LL | fn trait_object() -> &'static dyn ?const T { &S }
    |                                   ^^^^^^^^
 
+error: `?const` is not permitted in trait objects
+  --> $DIR/in-trait-object.rs:18:61
+   |
+LL | fn trait_object_in_apit(_: impl IntoIterator<Item = Box<dyn ?const T>>) {}
+   |                                                             ^^^^^^^^
+
 error: `?const` on trait bounds is not yet implemented
   --> $DIR/in-trait-object.rs:10:6
    |
@@ -22,5 +28,11 @@ error: `?const` on trait bounds is not yet implemented
 LL | fn trait_object() -> &'static dyn ?const T { &S }
    |                                   ^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: `?const` on trait bounds is not yet implemented
+  --> $DIR/in-trait-object.rs:18:61
+   |
+LL | fn trait_object_in_apit(_: impl IntoIterator<Item = Box<dyn ?const T>>) {}
+   |                                                             ^^^^^^^^
+
+error: aborting due to 6 previous errors