Update gix requirement from 0.67.0 to 0.68.0

Updates the requirements on [gix](https://github.com/GitoxideLabs/gitoxide) to permit the latest version.
- [Release notes](https://github.com/GitoxideLabs/gitoxide/releases)
- [Changelog](https://github.com/GitoxideLabs/gitoxide/blob/main/CHANGELOG.md)
- [Commits](GitoxideLabs/gitoxide@gix-v0.67.0...gix-v0.68.0)

---
updated-dependencies:
- dependency-name: gix
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

git-function-history-lib/Cargo.toml

@@ -24,7 +24,7 @@ chrono = "0.4.38"
 rayon = { version = "1.10.0", optional = true }
 cfg-if = "1.0.0"
 cached = { version = "0.54.0", optional = true }
-gix = { version = "0.67.0", default-features = false, features = [
+gix = { version = "0.68.0", default-features = false, features = [
     "max-performance-safe",
     "revision",
 ] }