chore: Bump gc-arena to 0.7.0, hashbrown to 0.17.1

[torokati44]

Description

Now that #24520 dropped hashbrown 0.15, let's move closer to perhaps dropping 0.16 as well.
After this, only Traverse-Research/gpu-allocator#302 and our regress fork (regras3) will pull it in. For the latter, upstream already allows 0.17, we'll just have to update our fork: ridiculousfish/regress@ec27815

Changelogs linked for convenience:

• https://github.com/kyren/gc-arena/blob/master/CHANGELOG.md
• https://github.com/rust-lang/hashbrown/blob/main/CHANGELOG.md

Testing

I hope automated tests + 🦀 "builds therefore correct" is enough here.

Checklist

• I, a human, have self-reviewed this PR and fully understand the changes within.
• I have made or updated tests where possible.
• All of my commits are properly scoped, compile successfully, and pass all tests.
• This PR does not make sense to split up into smaller PRs.
• An LLM was involved in the authoring of this code.

[danielhjacobs]

Approved based on the aforementioned "builds therefore correct" philosophy.