Fix test fallout

Author: jonas-schievink

src/test/compile-fail/cast-rfc0401.rs

@@ -87,7 +87,7 @@ fn main()
     //~^^ HELP through a usize first
 
     let _ = 42usize as *const [u8]; //~ ERROR casting
-    let _ = v as *const [u8]; //~ ERROR casting
+    let _ = v as *const [u8]; //~ ERROR cannot cast
     let _ = fat_v as *const Foo;
     //~^ ERROR `core::marker::Sized` is not implemented for the type `[u8]`
     let _ = foo as *const str; //~ ERROR casting

src/test/compile-fail/fat-ptr-cast.rs

@@ -24,7 +24,7 @@ fn main() {
     //~^^ HELP cast through a thin pointer
 
     // #22955
-    q as *const [i32]; //~ ERROR casting
+    q as *const [i32]; //~ ERROR cannot cast
 
     // #21397
     let t: *mut (Trait + 'static) = 0 as *mut _; //~ ERROR casting