chore: fix slice_regex name in Nargo.toml

[asterite]

Description

Problem

CI is failing for all PRs.

Summary

Additional Context

I wonder if we should have a CI script to check these? It's also strange that they go through CI.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[asterite]

Nevermind, I pushed a similar fix in #5607 which was already approved and is in the merge queue already.