Temporarily switch invalid_reference_casting lint to allow-by-default

compiler/rustc_lint/src/reference_casting.rs

@@ -12,6 +12,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,compile_fail
+    /// # #![deny(invalid_reference_casting)]
     /// fn x(r: &i32) {
     ///     unsafe {
     ///         *(r as *const i32 as *mut i32) += 1;
@@ -29,7 +30,7 @@ declare_lint! {
     /// `UnsafeCell` is the only way to obtain aliasable data that is considered
     /// mutable.
     INVALID_REFERENCE_CASTING,
-    Deny,
+    Allow,
     "casts of `&T` to `&mut T` without interior mutability"
 }