chore(deps): bump git2 from 0.20.4 to 0.21.0 in /robot-repo-automaton

Bumps [git2](https://github.com/rust-lang/git2-rs) from 0.20.4 to 0.21.0.
- [Changelog](https://github.com/rust-lang/git2-rs/blob/main/CHANGELOG.md)
- [Commits](rust-lang/git2-rs@git2-0.20.4...git2-0.21.0)

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

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

Author: dependabot[bot]

robot-repo-automaton/Cargo.lock

@@ -46,7 +46,7 @@ toml = "1.1"
 
 # Git operations
 # Using vendored-openssl to avoid system OpenSSL dependency (libssl-dev)
-git2 = { version = "0.20", features = ["vendored-openssl"], default-features = false }
+git2 = { version = "0.21", features = ["vendored-openssl"], default-features = false }
 gix = { version = "0.83", features = ["blocking-http-transport-reqwest-rust-tls"] }
 
 # S-expression parsing (for ERROR-CATALOG.scm)