fix panic on cargo xtask cts

[39ali]

Connections
#9313

Description
small fix for how we check for git version on mac
Testing

Squash or Rebase?

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[andyleiserson]

Thanks!