Update git2 requirement from 0.20 to 0.21

Updates the requirements on [git2](https://github.com/rust-lang/git2-rs) to permit the latest version.
- [Changelog](https://github.com/rust-lang/git2-rs/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/git2-rs/commits/git2-0.21.0)

---
updated-dependencies:
- dependency-name: git2
  dependency-version: 0.21.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Cargo.toml

@@ -15,7 +15,7 @@ serde_json = "1.0"
 serde_yaml = "0.9"
 dirs-next = "2.0"
 reqwest = { version = "0.13", features = ["json", "blocking"] }
-git2 = "0.20"
+git2 = "0.21"
 tokio = { version = "1", features = ["full"] }
 
 [dev-dependencies]