build(deps): bump git2 from 0.13.19 to 0.13.20 (#70)

Bumps [git2](https://github.com/rust-lang/git2-rs) from 0.13.19 to 0.13.20.
- [Release notes](https://github.com/rust-lang/git2-rs/releases)
- [Commits](rust-lang/git2-rs@0.13.19...0.13.20)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]