chore(deps): bump git2 from 0.20.4 to 0.21.0 in /shared-context

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]