Update git2 requirement from 0.18 to 0.20

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/git2-0.20.4/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/git2-rs/commits/git2-0.20.4)

---
updated-dependencies:
- dependency-name: git2
  dependency-version: 0.20.4
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Cargo.toml

@@ -12,7 +12,7 @@ clap = { version = "4.4", features = ["derive"] }
 chrono = { version = "0.4", features = ["serde"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
-git2 = "0.18"
+git2 = "0.20"
 tokio = { version = "1", features = ["full"] }
 
 [lib]