build: bump git2 from 0.20.3 to 0.20.4

Bumps [git2](https://github.com/rust-lang/git2-rs) from 0.20.3 to 0.20.4.
- [Changelog](https://github.com/rust-lang/git2-rs/blob/git2-0.20.4/CHANGELOG.md)
- [Commits](rust-lang/git2-rs@git2-0.20.3...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.lock

@@ -69,7 +69,7 @@ git-branchless-smartlog = { version = "0.10.0", path = "git-branchless-smartlog"
 git-branchless-submit = { version = "0.10.0", path = "git-branchless-submit" }
 git-branchless-test = { version = "0.10.0", path = "git-branchless-test" }
 git-branchless-undo = { version = "0.10.0", path = "git-branchless-undo" }
-git2 = { version = "0.20.3", default-features = false }
+git2 = { version = "0.20.4", default-features = false }
 glob = "0.3.3"
 indexmap = "2.13.0"
 indicatif = { version = "0.18.3", features = ["improved_unicode"] }