Allow dropping_copy_types lint in Miri tests

Author: Urgau

src/tools/miri/tests/fail/stacked_borrows/drop_in_place_retag.rs

@@ -3,6 +3,8 @@
 
 //@error-in-other-file: /retag .* for Unique permission .* only grants SharedReadOnly permission/
 
+#![allow(dropping_copy_types)]
+
 fn main() {
     unsafe {
         let x = 0u8;

src/tools/miri/tests/pass/drop_in_place.rs

@@ -2,6 +2,8 @@
 // valid when dropped. This test confirms that behavior.
 // This is not a stable guarantee!
 
+#![allow(dropping_copy_types)]
+
 use std::ptr;
 
 fn main() {