fix io_uring tests on kernel 5.4

Unsupported tests are now skipped on kernel 5.4:
```
uname -a
Linux d20 5.4.0-166-generic #183-Ubuntu SMP Mon Oct 2 11:31:37 UTC 2023 aarch64 aarch64 aarch64 GNU/Linux
zig test lib/std/std.zig --zig-lib-dir lib --main-mod-path lib/std 2>&1 | cat
709/2616 test.nop... OK
710/2616 test.readv... OK
711/2616 test.writev/fsync/readv... OK
712/2616 test.write/read... SKIP
713/2616 test.splice/read... SKIP
714/2616 test.write_fixed/read_fixed... OK
715/2616 test.openat... SKIP
716/2616 test.close... SKIP
717/2616 test.accept/connect/send/recv... SKIP
718/2616 test.sendmsg/recvmsg... OK
719/2616 test.timeout (after a relative time)... SKIP
720/2616 test.timeout (after a number of completions)... OK
721/2616 test.timeout_remove... SKIP
722/2616 test.accept/connect/recv/link_timeout... SKIP
723/2616 test.fallocate... SKIP
724/2616 test.statx... SKIP
725/2616 test.accept/connect/recv/cancel... SKIP
726/2616 test.register_files_update... SKIP
727/2616 test.shutdown... SKIP
728/2616 test.renameat... SKIP
729/2616 test.unlinkat... SKIP
730/2616 test.mkdirat... SKIP
731/2616 test.symlinkat... SKIP
732/2616 test.linkat... SKIP
733/2616 test.provide_buffers: read... SKIP
734/2616 test.remove_buffers... SKIP
735/2616 test.provide_buffers: accept/connect/send/recv... SKIP
736/2616 test.accept multishot... SKIP
```

0 files changed, 0 insertions, 0 deletions