Adjust some tests for invalid_reference_casting improvements

Author: Urgau

library/core/src/cell.rs

@@ -1893,7 +1893,8 @@ impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
 /// on an _exclusive_ `UnsafeCell<T>`. Even though `T` and `UnsafeCell<T>` have the
 /// same memory layout, the following is not allowed and undefined behavior:
 ///
-/// ```rust,no_run
+#[cfg_attr(bootstrap, doc = "```rust,no_run")]
+#[cfg_attr(not(bootstrap), doc = "```rust,compile_fail")]
 /// # use std::cell::UnsafeCell;
 /// unsafe fn not_allowed<T>(ptr: &UnsafeCell<T>) -> &mut T {
 ///   let t = ptr as *const UnsafeCell<T> as *mut T;

src/tools/miri/tests/fail/both_borrows/illegal_write1.rs

@@ -1,6 +1,8 @@
 //@revisions: stack tree
 //@[tree]compile-flags: -Zmiri-tree-borrows
 
+#![allow(invalid_reference_casting)]
+
 fn main() {
     let target = Box::new(42); // has an implicit raw
     let xref = &*target;

src/tools/miri/tests/fail/stacked_borrows/illegal_write3.rs

@@ -1,3 +1,5 @@
+#![allow(invalid_reference_casting)]
+
 fn main() {
     let target = 42;
     // Make sure raw ptr with raw tag cannot mutate frozen location without breaking the shared ref.

tests/ui/const-generics/issues/issue-100313.rs

@@ -9,7 +9,7 @@ impl <const B: &'static bool> T<B> {
         unsafe {
             *(B as *const bool as *mut bool) = false;
             //~^ ERROR evaluation of constant value failed [E0080]
-            //~| ERROR casting `&T` to `&mut T` is undefined behavior
+            //~| ERROR assigning to `&T` is undefined behavior
         }
     }
 }

tests/ui/const-generics/issues/issue-100313.stderr

@@ -1,8 +1,8 @@
-error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
+error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
   --> $DIR/issue-100313.rs:10:13
    |
 LL |             *(B as *const bool as *mut bool) = false;
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[deny(invalid_reference_casting)]` on by default