Update dev dependency selfsigned to v4, fix Node >=v24.5 compatibility, restore CI (#54634)

Summary:

CI fails after attempting to update to Node v24 (latest LTS) because our `dev-middleware` dev-only dependency `selfsigned` uses a default key size incompatible with the version of OpenSSL in Node>=24.5. We see lots of:

```
error:0A00018F:SSL routines::ee key too small
```

This was mitigated in OSS CI by pinning our Node tests to before v24.5: https://github.com/facebook/react-native/pull/53013

This default is raised upstream in https://github.com/jfromaniello/selfsigned/commit/bf687c80cfe125b7051c7b2f07e321289c037993 , this bumps to v4 which includes that fix, and removes the temporary mitigation above.

Changelog:
[Internal]

Reviewed By: cipolleschi

Differential Revision: D87643898