Rollup merge of #108558 - RalfJung:core-tests, r=thomcc

add missing feature in core/tests

#104265 introduced the `ip_in_core` feature. For some reason core tests seem to still build without that feature -- no idea how that is possible. Might be related to #15702? I was under the impression that `pub use` with different stability doesn't actually work. That's why `intrinsics::transmute` is stable, for example.

Either way, core tests fail to build in miri-test-libstd, and adding the feature fixes that.

r? ```@thomcc```

library/core/tests/lib.rs

@@ -67,6 +67,7 @@
 #![feature(slice_internals)]
 #![feature(slice_partition_dedup)]
 #![feature(ip)]
+#![feature(ip_in_core)]
 #![feature(iter_advance_by)]
 #![feature(iter_array_chunks)]
 #![feature(iter_collect_into)]