Bump git2 from 0.20.2 to 0.20.4

Bumps [git2](https://github.com/rust-lang/git2-rs) from 0.20.2 to 0.20.4.
- [Changelog](https://github.com/rust-lang/git2-rs/blob/git2-0.20.4/CHANGELOG.md)
- [Commits](rust-lang/git2-rs@git2-0.20.2...git2-0.20.4)

---
updated-dependencies:
- dependency-name: git2
  dependency-version: 0.20.4
  dependency-type: direct:production
...

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Author: dependabot[bot]