Bump git2 from 0.14.2 to 0.15.0

Bumps [git2](https://github.com/rust-lang/git2-rs) from 0.14.2 to 0.15.0.
- [Release notes](https://github.com/rust-lang/git2-rs/releases)
- [Commits](rust-lang/git2-rs@0.14.2...git2-curl-0.15.0)

---
updated-dependencies:
- dependency-name: git2
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Cargo.lock

@@ -67,7 +67,7 @@ walkdir = { version = "2.0", optional = true }
 bytesize = { version = "1.1.0" }
 
 [dependencies.git2]
-version = "0.14"
+version = "0.15"
 optional = true
 default-features = false