Update libgit2-sys requirement from 0.12.18 to 0.13.0

Updates the requirements on [libgit2-sys](https://github.com/rust-lang/git2-rs) to permit the latest version.
- [Release notes](https://github.com/rust-lang/git2-rs/releases)
- [Commits](https://github.com/rust-lang/git2-rs/commits/libgit2-sys-0.12.26)

---
updated-dependencies:
- dependency-name: libgit2-sys
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Cargo.toml

@@ -44,7 +44,7 @@ jobserver = "0.1.24"
 lazycell = "1.2.0"
 libc = "0.2"
 log = "0.4.6"
-libgit2-sys = "0.12.18"
+libgit2-sys = "0.13.0"
 memchr = "2.1.3"
 num_cpus = "1.0"
 opener = "0.5"