Upgrade gix for better commit message trailer parsing support/better diff slider processing

[Byron]

Relevant for #13247, #13048, #12948.

• wait for fix(gix-object): detect trailers when they are the sole body content GitoxideLabs/gitoxide#2514
• wait for Use imara-diff-v2 by default GitoxideLabs/gitoxide#2513 - do not wait for it, as it might cause use to require more changes, possibly, also the conflict-handling doesn't have to block on it.

[vercel]

@Byron is attempting to deploy a commit to the GitButler Team on Vercel.

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[Copilot]

Pull request overview

Updates the gix (gitoxide) git dependency to a newer upstream revision to pick up fixes/improvements for commit message trailer parsing and diff processing.

Changes:

• Bump the pinned gix and gix-testtools git revision in the workspace Cargo.toml.
• Regenerate Cargo.lock to reflect the updated git source for the gix* crate set.
• Adjust commit trailer extraction to use the updated gix trailer value ownership API (into_owned()).

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/gitbutler-repo/src/commit_message.rs	Adapts trailer value extraction to the updated gix API while preserving the existing commit message parsing behavior.
Cargo.toml	Updates the pinned git revision for gix and gix-testtools in tandem.
Cargo.lock	Updates locked git sources for gix and related crates to the new revision.