[workerd-cxx] fix nightly tests

not entirely sure why they fail for us but not for upstream

Author: mikea

tests/ui/missing_unsafe.stderr

@@ -1,9 +1,10 @@
 error[E0133]: call to unsafe function `f` is unsafe and requires unsafe function or block
  --> tests/ui/missing_unsafe.rs:4:12
   |
+1 | #[cxx::bridge]
+  | -------------- items do not inherit unsafety from separate enclosing items
+...
 4 |         fn f(x: i32);
-  |            ^        - items do not inherit unsafety from separate enclosing items
-  |            |
-  |            call to unsafe function
+  |            ^ call to unsafe function
   |
   = note: consult the function's documentation for information on how to avoid undefined behavior

tests/ui/ptr_unsupported.stderr

@@ -1,5 +1,5 @@
 error: C++ does not allow pointer to reference as a type
- --> tests/ui/ptr_unsupported.rs:6:38
+ --> tests/ui/ptr_unsupported.rs:6:42
   |
 6 |         fn get_ptr_to_reference<'a>() -> *mut &'a C;
   |                                          ^^^^^^^^^^