`tests/run-make/alloc-no-oom-handling` tests that `alloc` under
`no_global_oom_handling` builds and is warning-free.
Do the same for `core` to prevent issues such as [1].
Link: https://github.com/rust-lang/rust/pull/110649 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
