build(deps): update onig_sys to fix build on gcc 15

[luizfelmach]

What kind of change does this PR introduce?

Bug fix (build failure on Archlinux)

What is the current behavior?

The project fails to build on Arch Linux using GCC 15.

The failure is caused by an incompatibility in onig_sys, which does not compile correctly with GCC 15.
This issue is already tracked upstream in the rust-onig repository:

rust-onig/rust-onig#203

onig_sys is not a direct dependency of this project; it is a transitive dependency pulled in by ext_ai.

What is the new behavior?

The build succeeds on Arch Linux with GCC 15 after updating onig_sys to a newer version where the issue has been fixed upstream.

No application code was changed — only the affected indirect dependency was updated to restore compatibility.

Additional context

• The fix comes directly from the upstream rust-onig project.
• This PR updates a transitive dependency to resolve a toolchain-specific build failure.
• Other platforms and compilers are unaffected.